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Nice work. Thank you. New generation is very lucky. When I was an engineering student (30 years ago) we had only paper, pencil, books and blackboard. These kind of videos should be considered as a big revolution in education.
Yeah, I remembered how much trouble I did when I was 14 years old (in 1993) trying to have a comprehension of all those electrical phenomenon that are very easy to understand using animations nowadays.
I agree that this videos are astonishing useful and beautiful. However, there're evidence (my apologies for not find the source; I explain it below) that images associated with text are as good as animations, if not superior. This phenomenon is related with "brain effort" to learn the schema, concept or principle. I remember Derek Muller (Veritasium) discuss it in one of his videos, but as I search through his channel, I couldn'r find it. It is in one of his videos about education and learning. Edit: found it --> ua-cam.com/video/GEmuEWjHr5c/v-deo.html
@@GeovaniLopesDias yeah I actually learned about this phenomenon somewhere (probably from Derek too) that images and texts kinda force you to imagine stuff, use more brain power, and therefore remember stuff for longer. Animations, on the other hand, makes it easier for you to understand a concept, so you might be tricked to use less brain power, and there are more likely to forget stuff. But anyway, animations are a game-changer if you realized this phenomenon and have certain learn techniques to help you remember stuff. In the end I actually believe that the more effort you put in, the more you're gonna get out.
OMG! I've been studying all this stuff on my own and when I started investigating concepts around Resistance I came to a similar idea about the fallacy but couldn't articulate it since I didn't know enough. I'm so greatful that this video goes into it because I thought I was crazy lol!
Except water flowing in pipes is usually a non-linear relationship between flow rate and pressure drop, so it is more difficult to make the analogy mathematically accurate.
carultch. Not only that. The electric phenomena is tridimensional, happens in the space around the circuit. At any given instant half of the energy is in the space and half in the circuit. Actually the energy is flowing from the battery to the space and from the space to the conductor. The Voltage, the electric force, is not like a pressure pushing the electrons, the Voltage is a field in the space. The magnetic field is not a waste product of the electrons movement, magnetic field stores energy in the space! The energy is flowing from the space to the wire perpendicularly.
That's quite important... A lot of people use pipes to make analogy for electricity, which seems to be extremely convenient at first, but I think that now I understand why I wasn't able to grasp the concepts of electricity fully... Thanks!
I recently created a Patreon account for people who want to help support my channel. The link is on my UA-cam home page and in the video description up above. Also, in case, you have not already seen them, I uploaded several other videos recently. As always, for each video that you like, you can help more people find it in their UA-cam search engine by clicking the like button, and writing a comment. Lots more videos are coming very soon. Thanks.
+Eugene Khutoryansky These are such amazingly high quality videos. I'm shocked at how many high quality, illustrative videos you have on your channel. I'll see if I can donate a bit to your patreon account :). Keep up the awesome work. Mathematics and sciences are, in my humble opinion, the most beautiful and fulfilling study that one can engage in. Thanks for making it accessible to the massive amount of scientifically illiterate people.
+Eugene Khutoryansky I don't know what a patreon account is; but your videos have always been amazing and I think it's well worth donating a few bucks for all the value I get out of your channel.
+Physics Videos by Eugene Khutoryansky Your videos on electric circuits are awesome. I use them on a regular basis and my students love them. They really help to re-enforce what the text book is saying. Is it possible to make a video on Alternating Current and Alternating Current Circuits. The future Aircraft Technicians would greatly appreciate this.
+Physics Videos by Eugene Khutoryansky All the equations for physics are dependant to physical parameters. The viscosity, thermal conductivity, electrical conductivity and speed of light depend on the medium. Thus, ohm's law is correct, but one must apply differential form of equation to solve complex problems, not simplified form that is constant parameter solution of ohm's differential law.
"There are many examples in logic where a statement is always true simply because of the way in which we created our definitions for the words, and the statement doesn't actually tell us anything about the external world around us.This one of the logical fallacies we need to watch out for, both with regards to science and also with regards to life in general." Boom.
@@naveensundar4765 Let's look at the statement that immediately precedes that one: "The fact that the number that we get at any given time is always equal to the resistance of the material is simply due to the fact that this is how we defined the word 'Resistance' in the first place." Let's say we had workers packing apples in a factory. We can create a value for each worker called "productivity" (P), which is the number of apples (A) they packed in a given period of time, divided by the number of hours that they worked (T). P = A / T A worker whose productivity is 500 can pack 500 apples in one hour (seems pretty slow, but we'll ignore that). Next, we make an observation: if we know a worker's productivity (P), then we can predict how many apples (A) they can pack in a given amount of time (T). A = PT This is a valid observation, however we haven't actually learned anything. P was already derived from A and T, so deriving A from P and T doesn't tell us anything new about the nature of our factory. At best, in this exercise we have learned about the multiplication property of equality, which allowed us to re-arrange the factors to solve for a different variables. In which case, we've learned something new about math, but not about apples, time, or productivity. I believe Khutoryansky was referring to circular logic. For example, a society might decide that drinking alcohol is immoral, so they make a law against it. Now it is illegal. It is illegal because it is immoral. Now, imagine someone new enters the society, and they discuss alcohol with some of the locals. "If you like to drink alcohol, we will not accept you as a friend. Drinking alcohol is wrong." "Why is it wrong?" "Because it is illegal. Only an immoral person would want to do something that is illegal." Then it isn't a discussion about alcohol at all. They are simply deriving immorality from illegality, when illegality was originally derived from immorality. This is a closed loop, where no new information is allowed out or in. In fact, we can't trace the origin of the "immorality" label for alcohol. How did it come to be immoral in the first place? "The Law of the Immorality of Alcohol", then, isn't a new law in the scientific sense. It's just a logical derivation of the previous "The Law of the Illegality of Alcohol". I believe this was the intended point. Not specifically about alcohol, of course.
@@tom_something What about the equation for force then? Consider a mass, M, falling near earth's surface at acceleration g. We define force: F=Mg. But what if we did not actually know g, for whatever reason, and we knew M and F, then we could 'learn something new about the world' by finding g from g=F/M. But... Do we really learn something about the external world or just a construct of ours? We like to think of a force as a property of the physical world but that is ultimately based on acceleration and mass, and acceleration is based on time and velocity, which is based on position. The only 'tangible' things here are perhaps position, mass, and time. Does this make velocity, acceleration, and force a construct that is just as invented as resistance?
@@Nelson-sr2bi Yes, in fact. Something that would qualify as an actual law of physics would be, say, the Law of Conservation of Momentum, or the Law of Conservation of Energy. Neither of those laws are derivable from our definitions of momentum or energy (p = mv or e = 1/2mv^2 as an example), or are they definitions of some other variable. Those laws genuinely tell us something about the universe, which is what separates them from simple definitions like F=ma. By the way, just because we chose to define things like velocity and acceleration doesn't mean that they aren't real. After all, the laws I mentioned actually rely on our definitions of mass and velocity to be meaningful.
Khutoryansky's definition: "Physical laws tell us how the Universe works." ( 3:27 ) Ohm's Law tells us that the resistance of an object at a certain time is equal to the voltage across the object at that time divided by the current through the object at that time. Because of Ohm's Law, if you know two of the three values (1. Resistance 2. Voltage 3. Current) for a certain object at a certain time, then you can calculate the third value of the object at that time. It is possible to calculate and consequently know the third value because Ohm's Law tells us how the three values work in the Universe. Ohm's Law tells us how a part of the Universe works, and thus is a law by Khutoryansky's definition of a physical law. The Universe works in way that when the resistance of an object changes (whether by temperature or some other change in the object), current through the object changes because the voltage across the object remains the same. Ohm's Law tells us about this way that the Universe works. "the statement doesn't actually tell us anything about the external world around us." ( 5:29 ) The statement of Ohm's Law tells us how the resistance of an object, the voltage across the object, and the current through the object are related, like how the equation F = ma (Newton's Second Law) tells us how the force applied to an object will relate to the mass of the object and the acceleration of the object caused by that force. "There are many examples in logic where a statement is always true simply because of the way in which we created our definitions for the words, and the statement doesn't actually tell us anything about the external world around us." ( 5:19 ) F = ma is always true because we have defined force as a thing measured in joules where 1 joule = 1 kg * 1 m/s^2, so of course X joules will equal Y kg * Z m/s^2. My first two paragraphs apply the same way to Newton's Second Law. Read them with the terms replaced: [Newton's Second Law] tells us that the [force applied to an object] is equal to the [mass of the object] [multiplied] by the [acceleration of the object caused by that force]. Because of [Newton's Second Law], if you know two of the three values (1. [Force] 2. [Mass] 3. [Acceleration]) for a certain object at a certain time, then you can calculate the third value of the object at that time. It is possible to calculate and consequently know the third value because [Newton's Second Law] tells us how the three values work in the Universe. If I am missing something, please explain. I will try my best to understand.
+Blake Callahan, in the case of F = mA, force is defined independently of this equation. For example, we have laws for how forces on charged particles are generated as the result of electric and magnetic fields. On the other hand, in the case of R=V/I, resistance is defined entirely by this equation. F=mA relates how something which already has a definition (force) relates to other observable quantities. On the other hand, R=V/I does nothing other than to just create a definition for the quantity "V/I".
+Blake Callahan, in the case of an electromagnetic force, we have F = q[E + v x B]. This is just one example, as other types of forces have other equations.
+Eugene Khutoryansky I'm not sure I understand your logic regarding what makes a law. Newton tells us force is the time derivative of momentum. That's true, according to him. Then, we find other ways to calculate force, as you pointed out in your comment. But wouldn't it just be another way to calculate the time derivative of momentum? If you say Ohm's law is not a law because resistance is only a way to define V/I, wouldn't force just be another way to define dp/dt, thus making it not a law? I really liked your video, by the way. Great job!
Also, you seem to say Newton's laws are actual laws because there were other ways to measure it, like the electromagnetic force. But I think there weren't other ways to calculate force before Newton published his Principia. In that case, his equations only became actual laws (according to your definition) when other people came up with different ways to calculate dp/dt?
Exactly, even the voltage varies with the variation of the external resistance, due to the internal resistance of the real generator, the ohm law must be interpreted assuming the ideal case, the real case can always be traced to the summation of the ideal cases. Ohm's law is essential for calculating the circuit because it is very close to the ideal case.
The mentioned fallacy states that a law which has been formulated is a mathematical representation for a model that describes something observable in the real world. That one model works together with all the other models may seem like a coincidental happenstance to critics of science, but it actually is a beautiful hint that the 'laws' are just implications of higher abstractions. Some people say scientists act like there is only one truth and they know it. Maybe some scientists are that way. But the truth is, scientists just state that their model works and fits in the picture.
When showing a higher or lower value of resistor may be better by lengthening or shortening rather than make the resistor a smaller diameter for a smaller resistance; because typically a smaller diameter resistor does not indicate less resistance but more resistance. I also agree with a previous comment of "but that doesn't mean that the voltage drop across a ckt element is not proportional to the current flowing through it " Thank you for your animation and will looking for to an update.
Ohm's observation was that the apparent Potential drop across an ideal Resistor is proportional to the Current through it. So, V=RI would be the linear model accounting for V versus I data. Yet, one uses I-V characteristics, which gradient equals 1/R (conductance). This tells us how fast the charge transport can be through the Resistor. Hence, Resistance is a measure of the charge transport time! *R ~ t* Yet, in a real _ohmic_ resistor, temperature might increase with time, so the I-V slope changes, depending on the experimental procedure...
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+Blackyisacat, I am glad that these videos are getting to you in time. In the past, I had a person complain that the video was on a topic that he had just taken his final exam in, and that if the video had been released just a few days earlier, it would have helped him correctly answer the question that he missed.
Not only are these videos perfect visual presentations, but the final thoughts of this particular video was almost existential. :) Love your work, thanks.
Maybe she should've learned how to read resistor color codes.
6 років тому+2
Thank You for this video. People seem to think by solving the circuit is the same as understanding it, which is a fallacy that needs to be corrected. I've always was more interested in understanding a circuit & it's fundamentals which can be very hard to grasp because of how they describe it, for example, Ohm's law something you alluded to briefly in your video, you mention how it is not a actual law. Thank you for pointing that out.
What's presented here is a simplified _model_ of the V I circuit relationship. You can write a more accurate model that takes account of the many other factors, but this version is good approximation for most DC circuits. Temperature co-efficients are easily accounted for but AC circuits, and RF circuits in particular, are where things get trickier.
Exactly. It would be like arguing the existence of Newton's Second Law, and the Law of Universal Gravitation. Both laws are generalities of a larger picture. For instance, the Law of Universal Gravitation works for smaller objects, but does not accurately calculate the orbit of Mercury.
I really thank you. Your video is a simple and clear illustration of how voltage, resistance and current intensity interact. One can watch it OBSERVE, SEE how it works clearly. You are helping lots of people to really understand the basics of electricity. Thank you.
Ive spent hours upon hours trying to understand resistance and get an intuiative feel about how it worked and this video is the only one that got me to figure it out.
i have multiple accounts, and multiple times i would find your videos for mutiple reason. And, in all of those scenarios, i would like, subscribe and thank you. So here i am again: Thank you.
Ohms law can be stated for puplis more correctly for many devices as " the resistance of a metal device of constant temperature remains constant". And resistor can be defined " a device for which Ohms law is valid". In the transation to greek language I made sime small changes in terminology to make video "compatible" with greek educational school system and definitions.
Original statement that Ohms law is NOT a law is at best MISLEADING and at worst plain WRONG! Ohms law established formula that Resistance R is proportional to the resistivity of the material (constant but different for given materials, such as copper, aluminum, gold, etc.) and the length of the wire and inversely proportional to the cross-section of the wire. That is the indeed the Law that Gerhard Ohm found. The reason why the resistance changes with temperature is precisely due to increase of the length of the wire with temperature increase resulting in proportional increase of the resistance. So, it is indeed a LAW even when you considered temperature effect! My daughter has made an experiment for sixth grade class of verifying Ohms Law by using different materials, like copper and aluminum wire and changing their length and measuring the current for a given DC voltage source to verify the above formula for Ohms Law. In fact, for magnetic circuits, Ohms law serves beautifully to introduce the equivalent dual concept, the Reluctance of the magnetic circuit as proportional to permittivity of the magnetic material, and the length of the magnetic core and inversely proportional to the cross section of the magnetic core. The AC inductance is then defined simply as turns squared times the reluctance! Dr. Slobodan Cuk (former Professor of Electrical Engineering at Caltech and inventor of Power Electronics switching converters). See my videos on UA-cam.com/slobodancukTESLAco
The resistivity of a material is not constant, and that was my point. That is, even if you take the same length and width of the material, the total resistance may depend on temperature and a variety of other factors. It is just that for materials like aluminum and copper, this change is very small. But for the material used in thermistors, this change is very large, and this can't be explained in terms of the length or cross section of the material changing, but needs to be explained in terms of a change in the resistivity itself.
I understood the point about the controversy caused by the use of the word "law". Since my primary formation is as engineer, I am used to call it "Ohm's law", therefore in any mathematical relationship, a proportionality constant is used to fit the model to an "operational range". In this case, the R value is not really a constant that groups all the non-linear effects, moreover its definition only involves the V and I. For this reason, after the explanation of Eugene, I agree that it is not really a law, it is just a concept that works at a very basic level. Finally, it is importat to keep cuestionating all the knowledge, and also our own learning.
My high school teacher told us to think of resistance intuitively as of the amount of collisions that the electrons experience as they go through the wire, for example.: resistance increases with temperature because the atoms in the wire (or within the resistors) are vibrating more and thus are more likely to impede the path of the electrons; also the longer the resistor or the smaller its cross-sectional area, the more collisions. Is there any way to relate this approach to the existing definition of resistance as voltage/current ?
I have read somewhere that electric "flow" is dependent on the surface of the conductor and electricity spreads due to changes in the magnetic field surrounding the wire....
I, too, don't want to seem contrite, but I have to correct the claim of a logical fallacy on tried-and-true physics. Ohm's law actually is a vector electro-magnetics equation. Since I can't write Vector notation here, assume that capital letters are vectors in the following, and I'll write out the Greek letters, and T is temperature. J=sigma(T)*E where J is the current density, Sigma is the conductivity that is a function of temperature, and E is the electric field. First thing to point out is that the conductivity of a material is temperature dependent, and that temperature dependence is taken into account in Ohm's law. Second thing to point out is that the version of Ohm's law used in circuit analysis is a simplified scalar form, with a few important assumptions and simplifications. That does not mean that the scalar form used in circuit analysis is incorrect. Furthermore, just because one observes and minor inconsistency in a heavily simplified application of a physics edict does not mean that physics edict is incorrect.
The Feynmann lecture mentioned many times in the comments discusses that even the most fundamental laws are only approximations becouse reality never gets so simple as to be completly described by mathematical equations. On the other hand we have uncovered LAWs which are almost universal becouse they are approximations of some fundamental phenomenon underlying almost all physical phenomena. In my interpretation this video suggets that there is no such fundamentum behind Ohms Law. BTW I have read somewhere that electric "flow" is dependent on the surface of the conductor and electricity spreads due to changes in the magnetic field surrounding the wire.... Is it so? If yes - is there a YT animation on that?
I think you missed the point of Ohm's law. The law doesn't say that the voltage divided by the current is the resistance. It states that: The current through a conductor between two points is directly proportional to the voltage across the two points. Now, the constant of proportionality is what we call the resistance. . In other words: Ohm's law states: V is directly proportional to I Definition of the resistance is R=V/I
Physics Videos by Eugene Khutoryansky This is already known.. Same as Hook's law (for example) is an approximation and is not applied in all cases to all elastic objects. But your misunderstanding of the law is in your interpretation of the law as merely the definition of resistance..It is not that: as I said above. So it is a "law" (limited .. I know !) and not a "definition" as you said in the video.
+Heliocentric I think the misunderstanding here about Ohm's law with respect to this video was that it is a physical principle or a concept that electromotive force (voltage in short no pun intended) pushes the current (which is the amperage) through a resistor or a device (resistance) across a circuit. It is not the formula E = IR nor the direct and inverse proportionality of the 3 physical entities/information.
The confusion lies in the conflation of 'resistor' and 'resistance'. V = I • R is indeed true regardless of the resistor used and the condition it is in. The R represents resistance, not resistor.
1. There are preconditions to this law such as 'under constant temperature' which is to imply that the law would be talking about a simplified model of real life system like most laws in physics. Therefore, it is to be used more as a guideline rather than as a law beyond textbooks. 2. The statement is also not R=V/R. Ohm's law statement is that current flowing (the effect) is proportional to voltage (the cause) across the resistor. Resistance is only the constant of proportionality to represent the law as an equality. Therefore, the law is not responsible for a variable resistance. Even under changing conditions (under the preconditions mentioned in 1), the law still holds.
V=I*R is not really Ohm's Law. V=I*R is how we define resistance, as you have clearly stated. A better formula for Ohm's law is dR/dV = 0 and dR/di = 0. Ohm's law is that resistance is not a function of electrical operating conditions. Given a resistor of a material that doesn't change identity or geometry, that is maintained at a particular temperature by an independent system, its ratio of voltage to current is the same no matter what the voltage or current is. That is what Ohm's law is.
A more accurate way to explain that Ohm's law is not Universal is with negative resistance. This can occur in plasmas and electronic components where the current-voltage relation is highly nonlinear. See en.m.wikipedia.org/wiki/Negative_resistance
You are right as this essentially is a DC circuit. The resistor upper terminal is positive and the lower one negative. Or the lecturer tried to draw the "counter vector" with same colour. In my ham radio training in the early 1980's the voltage drop was explained to be a counter vector of same size but opposite direction as the voltage measured accross the resistor. At that time they taught that the current flowing thru the load resistor gives rise to the voltage drop (counter vector) which has to be substracted from the battery voltage.
Ohm's law works fine for metals at low current densities. The temperature effect is a separate issue. Ohm's law des not work for non-metals, semimetals, semiconductors, electrolytes, gases or metals at high current densities. It has to be modified for alternating currents to take account of capacitive and inductive reactance. But for basic electrical engineering and electronics it is still a very useful formula.
I find it hard to believe that someone could learn these concepts easier by not seeing these diagrams. I know there are people who fair easier with audial or tactile stimulation when it comes to learning (or so it seems.) Let's say we take any person with all their senses intact and present to them these concepts in only one way: audial, tactile, or visual. It's hard for me to believe that someone could better learn about these physical phenomena with audial or tactile information but no visual. I'm not even that visual myself. For instance, I listen to audiobooks a lot and most of the time, I don't paint a clear picture in my head about the stories or topics being presented (probably because I'm usually driving lol.) I can still understand what's being said and ponder upon it without visualization. Still, I find these visual presentations about physics to be far more helpful than just listening or just physically tinkering or rearranging. I know I'm being biased about this but I would like to hear the perspective of someone who, if they only had one form of stimulation to choose from, would learn better with some stimulation other than visual.
Hi Eugene, during my studies in high school I would have needed these kind of representations of how electicity works. Now, all thank to you, I can put images and representations on what I know of electricity, and it makes way more sense
so hold on. when the resistance changes as the resistor heats up, why does this change "ohms law" isnt that only changing one variable of the equation continuously, thereby changing the answer continuously? i dont know but doesnt it seem like ohms law is ever changing, along with the resistance?
Hence why the its Voltage/Current = Resistance and not Voltage/Current = Original resistor value. the clue is in the name, if the resistance alternates, more current flows, and the increase in current flow across it is proportional to the resistors deterioration. Therefore the law still applies :D
This is a lovely demonstration, but isn't ohms law " The PD of a metallic conductor is directly proportional to the current flowing through it, AT A CONSTANT TEMPERATURE"? So ohms law actually addresses the change in temp, which is why a filament bulb is a non ohmic device.
Ok so in any case anyone is still in the comments. Could someone clarify this for me? What this video is impling is that: "Ohm law does not define resistance outside of it, therefore it's not a law". In the principal example of Newton's second Law, that even without (F=M*a)acceleration could still be defined in some way. The reason of not being a law is that the Resistance does not have a *constant* for the actual resistance, since it would decreasse with temperature. So if in some way we define a constant for the *material* with the resistance at certain temperature; and another one for the *amount that it changes with temperature* and relate that through the current passing. Then it would be defined as a law? Like: *R = Constant - ValueOfChange*DiferenceInTemperature.* This way we could explain how the material change, and find a way to discover temperature by the new resistance. I mean this is what we did with most atomic numbers. Found the value for a constant and related that with somethin. Molar mass and avogrados.
The Feynmann lecture mentioned many times in the comments states that even the most fundamental laws are only approximations becouse reality never gets so simple as to be completly described by mathematical equations. On the other hand we have uncovered laws which are universal becouse they are approximations of some fundamentum underlying almost all physical phenomena. In my interpretation this video tells that there is no such fundamentum behind Ohms Law. For example as far as I know there is no universally valid the "R = Constant - ValueOfChange* DiferenceInTemperature" equation. If there is such a constant valid for at least all electro-conductive metallic material than perhaps Ohms law would indicate some fundamental quality of those materials. I have forgotten a lot about physics so maybe such a constant exists :)
to have a meaningful existence a soul is like electron, it must pass many resistors and keep finding the return path even through the hardest resistance or jumping around various frequencies to make a complete journey in any given circuit (life time). That is the universal law.
Are you saying Ohm's Law isn't a law because ultimately is just a definition? In that case, would Newton's second law of motion just be a definition of force and not a law?
+didles123, Newton's second law of motion does not suffer from this problem because "Force" is already defined independently of Newton's second law. For example, we have equations describing how forces are generated on charged particles due to electric and magnetic fields, and this is separate from Newton's laws. Newton's second law relates how this force that is generated will relate to the object's acceleration, and hence this is a statement about the external universe around us, and not merely a matter of semantics.
+Eugene Khutoryansky Although I have never heard it put as plainly before, I think your statement about Ohm's Law makes sense, and that distinguishing between it and Force = Mass times acceleration is being timid. I have heard it said that the force law mutually defines force and mass. We do not know what the property mass is except for the acceleration produced by some force. And we do not know what a force is except for the acceleration of some mass. But in fact both equations slip something by our content detectors, while being definitions. Thus if we combine 7 (or whatever) equal masses and subject them to the same force as one mass, their acceleration is claimed to be one seventh. If we take 7 equal resistances in series and subject them to the same voltage as one, the current is claimed to by one seventh. It is logically possible that 7 equal masses combined, and subjected to the same force as one, would accelerate differently than one seventh as much. We could just claim that the true mass was not found by adding, and figure the mass. It is logically possible that 7 equal resistances in series subjected to the same voltage as one would conduct a current different than one seventh. We could just claim that resistances did not add, and figure the resistance.
+binnacle true-north We have this apparent phenomenon in Newton's second law of motion as well. Externally applied force F is not always proportional to ma. This is always the work of an external retarding force (not accounted for in "your" simplistic calculation), but it does happen.
Not convincing. R=V/I is not the definition of resistance. It is a physical law that relates those three properties of a system. Arguing that it isn't a fact of the universe because the resistance of a material doesn't stay constant is just ignorance of the more complex relationships involved. The actual definition of resistance is R=resistivity •length/area. All three of those variables can be affected by temperature, and resistivity also depends on material composition. I suppose you could try the same game by substituting the definition of resistance into Ohm's law: r•L/A = V/I (here I am using r for resistivity) and then define resistivity as r = V•A/(L•I). But that doesn't stop resistivity from being a real property of a substance. The "definition" gives a way to measure resistivity. In principle, at least, resistivity could be predicted from more fundamental physical theory.
Wow, very easy to understand these things explained things better than my instructors or teachers in college where they just read the books or what's inside the books in front without fully understanding the idea behide it and at the end we suffer. Thank you so much for making these kind of contents please continue doing
Johannes Sjolte I thought the same, but there is one difference. Both laws share the fact that you can define a new physical parameter, mass or resistance. But in Ohm's Law you have some materials that doesn't obey it, while in the other case every object has its mass remaining constant. But, that never happens actually, because of Special Relativity… Therefore… Ohm's Law is fine, but has that particularity which other laws doesn't have.
There is always in everything we generally assume. We must assume for something to be right. That is generally speaking about language. Language is a memory we all share. We can have different understanding of words, we might associate words with each other, and we might have strong or weak feeling connected to words. Without knowing the meaning of words before hand we cannot use unknown words to communicate with others. Just like you does not understand other languages when spoken. When it comes the subject of resistance: without further information and without giving it context. The formula of resistance is a simplified version of reality of resistance, in other word incorrect when it comes to accuracy. We need to assume temperature is included when calculating voltage of material for the formula to be right. Maybe we can get the right resistance with high accuracy if we take material purity of the conductor, absolute mass of material, absolute electron charge, molecular structure of the conductor, and take into consideration molecular structural change of the conductor during operation, then we can get more accurate resistance. But we are not much interested to include all the measurements for general application. The formula of ohm is a workable formula for general use, but not for quantum purposes where nano accuracy is demanded. Depending on demanded accuracy of calculation, the formula as it stands in my view does not qualify as a law. Since it does not include needed details to make it right and indisputable. It lacks information to make itself complete. Feel free to correct me.
I summon thee Eugene of Physics Videos by Eugene Khutoryansky or anyone who can help :) what about defining Resistance in terms of resistivity , length and Area. Now one would say resistivity is self defined But no we can also relate it to fundamental physical quantities like mass of an electron , charge of an electron , relaxation time and number charge density(no. of electrons per unit volume). (further doubts) Isn't this the reason why Ohm's law specifically states that it's under constant temperature and physical conditions. And I LOVE your videos , IT FEELS SO GOOD VISUALIZING EVERYTHING , thanks so much for all your efforts.(TOO GOOD)
That's the reason why current is same in series circuit. The Resistors reduce the voltage and so, as I=V/R, so reduced voltage will automatically result in reduced current! As less potential difference will cause lesser attraction and slow the current down.
Some comments and facts: When Ohm did this finding, there was no knowlege of electron or inside of atoms. Ohm found out that resistance is constant for metallic coductors, mainly copper, iron. He knew that resistance depends on temperature. There was not found yet the law of conservation of energy. Many other things were not known. We use nowadays resistance for example radiation resistance of dipoleantenna is 70 ohms. It's a feature of space, not any wireconductor. Explanation for electrons movement in conductor is quite complicated. It would be interesting to animate this properly.
I was not aware of the history. Thanks for the information. I will add the movement of electrons in conductors to my list of topics for future videos. Thanks.
I am not sure the stated reason ohms law is not a law of the universe is important enough to not call it a law of the universe. Maybe Ohms law could reformulated and thus not fundamental, but derived from other laws. But, the video did not convince me of the distinction it was attempting to make. The argument sounded similar to arguing that acceleration is not a law of the universe because a rocket expels mass would have a changing acceleration. It seems to me that the flaw in this kind of argument is that both ohms law and newton's law were respectively for instantaneous values of resistance and acceleration, not if their values change over time with different inputs. If we accept F=Mass*acceleration is a fundamental law of the universe, then why cant we accept that Acceleration=Force/Mass is the same law, just stated another way. If im in a rocket one moment the force I feel changes over time because the mass in my rocket is changing. This distinction on changing over time is seems unimportant. Besides, not all ohms are resistance that create heat. 10Vac supplied to a 1 om resistor will create 10 watts of heat as it allows 10 amps of current to flow. While 1 ohm of either Inductive or captive impedance will also limit current to 10 amps, but it does not loose any energy to heat, especially if the whole circuit is made of superconducting materials.
That argument is possible, and Feynman was worried he created definitions without proving their equivalence, and made an entire lecture about it: www.feynmanlectures.caltech.edu/I_12.html. Newton does really just define Force in the end, to be m*a. But showing equivalences such as F = GMm/r/r forces reality to behave in certain ways. Ohm's law is a property of most metals and is still at times inaccurate to degrees that can be felt. MOSFETs wildly disobey Ohm's law. LEDs disobey Ohm's Law quite notably due to heat. Op Amps also wildly disobey Ohm's law.
the reason for increased current flow is because of ohms law , and the formula for resistors in parallel. remember that if you had a 10 a 20 a 30 and a 40 ohm resistors in parallel, the total resistance is always smaller than the smallest. In this case the total resistance being 4.807 ohms
considering ohms law came from observing electrical circuits, it seems to tell us something about the universe. I^2r certainly does and its by definition as well.
"Having more resistors is like having a smaller resistance." This choice of words illustrates exactly why I don't understand that splitting up the track increases the current.
Imagine being in a duel with swords. As long as the other person resists you sword attacks, you can't hit him. Hitting him really means getting through his blocking. If the other person resists your attacks as strongly as you attack, you won't be able to hit him. But when you do hit him, you hit him once at one time. In the above case, your opponent/resistance is really strong and you barely pass any hits. In another case, you have three weak opponents who are not strong, so you can hit them much easier than it is to hit a strong blocker. Similarly, the electricity that passes through three weak opponents (resistors) has an easier time getting through than the electricity that tries to get through a strong opponent (resistor).
@@excitedaboutlearning1639 The thing is, they're saying that 3 STRONG "opponents" is like having 1 WEAK "opponent". I think the trick is that you can "attack" them all at the same time but it's still counter-intuitive.
I absolutely love these videos, they are beautiful in presentation whilst perfectly coupled with simplicity in explanation ...I wish I had access to this material as an Apprentice Electrician 30 years ago. It would have sped up my theory learning curve significantly. Amazing job....thank you
Yes, thank you. Some straight answers for once. I don't know why there is all of this misinformation when learning things like this. I'll have to check out your other videos. Thanks again.
Totally love your videos, they take something that may seem so abstract at first and turns it into a concrete and visual explanation that is incredibly helpful when studying physics. Thanks again!
What's your point exactly? As the resistance changes (due to temperature in this case), the current (or voltage) will adjust accordingly. Ohms law is not broken.
That's like to say "The Gonzales law says that a velocity of any particule is equal to the space it goes divided by the time it took", but that is exactly the way we define the velocity.
If a dummy like me can through animations and slow concise explanation take on board these concepts in energy, then it's possible for anyone to understand and grasp what is being taught here in these videos. Bora Metin ( 2 comments below this one ) is correct. This is a revolution in education. Thank you. You have a new Subscriber.
These animations are stunning! You make it easy to understand Ohm's Law. But personally, even at 2x speed, I find the video to be extremely slow. I guess that it makes these videos perfect for teachers in physics class, as they don't need to pause the animation during an explanation. Good work, keep it up :)
If ohms law is a definition.. Then newtons second law must also be a definition for term called force.. It will not define nature of universe but defines what is force.. So newtons 2nd law is also a definition.. Is it...
No, because we have definitions for the word "force" that are independent of Newton's second law. For examples, there are definitions that tell us how a force on a charged particle is created from electric and magnetic fields. Newton's second law then tells us how this force relates to mass and acceleration, for which we also already have independent definitions. By contrast, there is no independent definition for "resistance" (or "resistivity" / "conductivity"), other than ohm's law.
Feynman would be proud. It takes a critical mind to notice that knowing the name of something is not the same as knowing something about the character of nature. We must always be careful to distinguish the two, especially when things get complicated in physics and there are so many names of things. Knowing the names helps you communicate, but it doesn't contribute to a true understanding of nature!
Almost everything we use is more complicated than we think. Unfortunately this video does a disservice to students in my opinion. It's implying that a fundamental equation used in electronics is wrong or invalid.
A truly fantastic and novel way to educate the youth. When I was a youth I struggle to understand electric circuit theory; oh how I wish teaching material such as this channel were available!
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Ok?
I guess this is quality content. Thanks for the info on subtitles but I already knew it
@@JjMn1000 how dare you to say ' I guess'. It is quality content
Thank you Eugene 👍👍👍
Are you using Manim or using other softwares?
Nice work. Thank you. New generation is very lucky. When I was an engineering student (30 years ago) we had only paper, pencil, books and blackboard. These kind of videos should be considered as a big revolution in education.
Thanks.
Yeah, I remembered how much trouble I did when I was 14 years old (in 1993) trying to have a comprehension of all those electrical phenomenon that are very easy to understand using animations nowadays.
i thought it was 40 years ago?
I agree that this videos are astonishing useful and beautiful. However, there're evidence (my apologies for not find the source; I explain it below) that images associated with text are as good as animations, if not superior. This phenomenon is related with "brain effort" to learn the schema, concept or principle.
I remember Derek Muller (Veritasium) discuss it in one of his videos, but as I search through his channel, I couldn'r find it. It is in one of his videos about education and learning.
Edit: found it --> ua-cam.com/video/GEmuEWjHr5c/v-deo.html
@@GeovaniLopesDias yeah I actually learned about this phenomenon somewhere (probably from Derek too) that images and texts kinda force you to imagine stuff, use more brain power, and therefore remember stuff for longer. Animations, on the other hand, makes it easier for you to understand a concept, so you might be tricked to use less brain power, and there are more likely to forget stuff. But anyway, animations are a game-changer if you realized this phenomenon and have certain learn techniques to help you remember stuff. In the end I actually believe that the more effort you put in, the more you're gonna get out.
OMG! I've been studying all this stuff on my own and when I started investigating concepts around Resistance I came to a similar idea about the fallacy but couldn't articulate it since I didn't know enough. I'm so greatful that this video goes into it because I thought I was crazy lol!
Thanks. I am glad you liked my video.
Now I finally understood why resistors in parallel gives less recistance.
Glad I was able to help.
Xremote. Please don't do it. You'll ruin the understanding of what is electricity forever.
Except water flowing in pipes is usually a non-linear relationship between flow rate and pressure drop, so it is more difficult to make the analogy mathematically accurate.
carultch. Not only that. The electric phenomena is tridimensional, happens in the space around the circuit. At any given instant half of the energy is in the space and half in the circuit. Actually the energy is flowing from the battery to the space and from the space to the conductor. The Voltage, the electric force, is not like a pressure pushing the electrons, the Voltage is a field in the space. The magnetic field is not a waste product of the electrons movement, magnetic field stores energy in the space! The energy is flowing from the space to the wire perpendicularly.
That's quite important... A lot of people use pipes to make analogy for electricity, which seems to be extremely convenient at first, but I think that now I understand why I wasn't able to grasp the concepts of electricity fully... Thanks!
I recently created a Patreon account for people who want to help support my channel. The link is on my UA-cam home page and in the video description up above. Also, in case, you have not already seen them, I uploaded several other videos recently. As always, for each video that you like, you can help more people find it in their UA-cam search engine by clicking the like button, and writing a comment. Lots more videos are coming very soon. Thanks.
+Eugene Khutoryansky These are such amazingly high quality videos. I'm shocked at how many high quality, illustrative videos you have on your channel. I'll see if I can donate a bit to your patreon account :). Keep up the awesome work. Mathematics and sciences are, in my humble opinion, the most beautiful and fulfilling study that one can engage in. Thanks for making it accessible to the massive amount of scientifically illiterate people.
+Chris Johnston, thanks for that really great compliment about my videos, and I really appreciate the donation. Thanks.
+Eugene Khutoryansky I don't know what a patreon account is; but your videos have always been amazing and I think it's well worth donating a few bucks for all the value I get out of your channel.
+Physics Videos by Eugene Khutoryansky Your videos on electric circuits are awesome. I use them on a regular basis and my students love them. They really help to re-enforce what the text book is saying. Is it possible to make a video on Alternating Current and Alternating Current Circuits. The future Aircraft Technicians would greatly appreciate this.
+Physics Videos by Eugene Khutoryansky All the equations for physics are dependant to physical parameters. The viscosity, thermal conductivity, electrical conductivity and speed of light depend on the medium. Thus, ohm's law is correct, but one must apply differential form of equation to solve complex problems, not simplified form that is constant parameter solution of ohm's differential law.
"There are many examples in logic where a statement is always true simply because of the way in which we created our definitions for the words, and the statement doesn't actually tell us anything about the external world around us.This one of the logical fallacies we need to watch out for, both with regards to science and also with regards to life in general."
Boom.
can YOU please elaborate? THANKS.
@@naveensundar4765 Let's look at the statement that immediately precedes that one:
"The fact that the number that we get at any given time is always equal to the resistance of the material is simply due to the fact that this is how we defined the word 'Resistance' in the first place."
Let's say we had workers packing apples in a factory. We can create a value for each worker called "productivity" (P), which is the number of apples (A) they packed in a given period of time, divided by the number of hours that they worked (T).
P = A / T
A worker whose productivity is 500 can pack 500 apples in one hour (seems pretty slow, but we'll ignore that).
Next, we make an observation: if we know a worker's productivity (P), then we can predict how many apples (A) they can pack in a given amount of time (T).
A = PT
This is a valid observation, however we haven't actually learned anything. P was already derived from A and T, so deriving A from P and T doesn't tell us anything new about the nature of our factory. At best, in this exercise we have learned about the multiplication property of equality, which allowed us to re-arrange the factors to solve for a different variables. In which case, we've learned something new about math, but not about apples, time, or productivity.
I believe Khutoryansky was referring to circular logic. For example, a society might decide that drinking alcohol is immoral, so they make a law against it. Now it is illegal. It is illegal because it is immoral. Now, imagine someone new enters the society, and they discuss alcohol with some of the locals.
"If you like to drink alcohol, we will not accept you as a friend. Drinking alcohol is wrong."
"Why is it wrong?"
"Because it is illegal. Only an immoral person would want to do something that is illegal."
Then it isn't a discussion about alcohol at all. They are simply deriving immorality from illegality, when illegality was originally derived from immorality. This is a closed loop, where no new information is allowed out or in. In fact, we can't trace the origin of the "immorality" label for alcohol. How did it come to be immoral in the first place? "The Law of the Immorality of Alcohol", then, isn't a new law in the scientific sense. It's just a logical derivation of the previous "The Law of the Illegality of Alcohol".
I believe this was the intended point. Not specifically about alcohol, of course.
@@tom_something Thanks.MIND=BLOWN
@@tom_something What about the equation for force then? Consider a mass, M, falling near earth's surface at acceleration g. We define force: F=Mg. But what if we did not actually know g, for whatever reason, and we knew M and F, then we could 'learn something new about the world' by finding g from g=F/M. But... Do we really learn something about the external world or just a construct of ours? We like to think of a force as a property of the physical world but that is ultimately based on acceleration and mass, and acceleration is based on time and velocity, which is based on position. The only 'tangible' things here are perhaps position, mass, and time. Does this make velocity, acceleration, and force a construct that is just as invented as resistance?
@@Nelson-sr2bi Yes, in fact.
Something that would qualify as an actual law of physics would be, say, the Law of Conservation of Momentum, or the Law of Conservation of Energy. Neither of those laws are derivable from our definitions of momentum or energy (p = mv or e = 1/2mv^2 as an example), or are they definitions of some other variable. Those laws genuinely tell us something about the universe, which is what separates them from simple definitions like F=ma.
By the way, just because we chose to define things like velocity and acceleration doesn't mean that they aren't real. After all, the laws I mentioned actually rely on our definitions of mass and velocity to be meaningful.
Resistance is futile!
Like your life
@@adrians.4311 like every-body`s life... :)
Hey, thats MY line!
Khutoryansky's definition: "Physical laws tell us how the Universe works." ( 3:27 )
Ohm's Law tells us that the resistance of an object at a certain time is equal to the voltage across the object at that time divided by the current through the object at that time.
Because of Ohm's Law, if you know two of the three values (1. Resistance 2. Voltage 3. Current) for a certain object at a certain time, then you can calculate the third value of the object at that time. It is possible to calculate and consequently know the third value because Ohm's Law tells us how the three values work in the Universe.
Ohm's Law tells us how a part of the Universe works, and thus is a law by Khutoryansky's definition of a physical law. The Universe works in way that when the resistance of an object changes (whether by temperature or some other change in the object), current through the object changes because the voltage across the object remains the same. Ohm's Law tells us about this way that the Universe works.
"the statement doesn't actually tell us anything about the external world around us." ( 5:29 )
The statement of Ohm's Law tells us how the resistance of an object, the voltage across the object, and the current through the object are related, like how the equation F = ma (Newton's Second Law) tells us how the force applied to an object will relate to the mass of the object and the acceleration of the object caused by that force.
"There are many examples in logic where a statement is always true simply because of the way in which we created our definitions for the words, and the statement doesn't actually tell us anything about the external world around us." ( 5:19 )
F = ma is always true because we have defined force as a thing measured in joules where 1 joule = 1 kg * 1 m/s^2, so of course X joules will equal Y kg * Z m/s^2.
My first two paragraphs apply the same way to Newton's Second Law. Read them with the terms replaced:
[Newton's Second Law] tells us that the [force applied to an object] is equal to the [mass of the object] [multiplied] by the [acceleration of the object caused by that force].
Because of [Newton's Second Law], if you know two of the three values (1. [Force] 2. [Mass] 3. [Acceleration]) for a certain object at a certain time, then you can calculate the third value of the object at that time. It is possible to calculate and consequently know the third value because [Newton's Second Law] tells us how the three values work in the Universe.
If I am missing something, please explain. I will try my best to understand.
+Blake Callahan, in the case of F = mA, force is defined independently of this equation. For example, we have laws for how forces on charged particles are generated as the result of electric and magnetic fields. On the other hand, in the case of R=V/I, resistance is defined entirely by this equation. F=mA relates how something which already has a definition (force) relates to other observable quantities. On the other hand, R=V/I does nothing other than to just create a definition for the quantity "V/I".
+Eugene Khutoryansky What is the definition of force independent of F = ma?
+Blake Callahan, in the case of an electromagnetic force, we have F = q[E + v x B].
This is just one example, as other types of forces have other equations.
+Eugene Khutoryansky I'm not sure I understand your logic regarding what makes a law. Newton tells us force is the time derivative of momentum. That's true, according to him. Then, we find other ways to calculate force, as you pointed out in your comment. But wouldn't it just be another way to calculate the time derivative of momentum?
If you say Ohm's law is not a law because resistance is only a way to define V/I, wouldn't force just be another way to define dp/dt, thus making it not a law?
I really liked your video, by the way. Great job!
Also, you seem to say Newton's laws are actual laws because there were other ways to measure it, like the electromagnetic force. But I think there weren't other ways to calculate force before Newton published his Principia. In that case, his equations only became actual laws (according to your definition) when other people came up with different ways to calculate dp/dt?
Ohms law also states .....provided that the temp remains constant
Exactly, even the voltage varies with the variation of the external resistance, due to the internal resistance of the real generator, the ohm law must be interpreted assuming the ideal case, the real case can always be traced to the summation of the ideal cases. Ohm's law is essential for calculating the circuit because it is very close to the ideal case.
The mentioned fallacy states that a law which has been formulated is a mathematical representation for a model that describes something observable in the real world. That one model works together with all the other models may seem like a coincidental happenstance to critics of science, but it actually is a beautiful hint that the 'laws' are just implications of higher abstractions.
Some people say scientists act like there is only one truth and they know it. Maybe some scientists are that way. But the truth is, scientists just state that their model works and fits in the picture.
You are helping millions of students around the world..........................................never stop
When showing a higher or lower value of resistor may be better by lengthening or shortening rather than make the resistor a smaller diameter for a smaller resistance; because typically a smaller diameter resistor does not indicate less resistance but more resistance.
I also agree with a previous comment of "but that doesn't mean that the voltage drop across a ckt element is not proportional to the current flowing through it "
Thank you for your animation and will looking for to an update.
You would have to chnge the simulated visual representation from a cricked line into
a tunnel. I find the line repr. very useful.
Ohm's observation was that the apparent Potential drop across an ideal Resistor is proportional to the Current through it. So, V=RI would be the linear model accounting for V versus I data. Yet, one uses I-V characteristics, which gradient equals 1/R (conductance). This tells us how fast the charge transport can be through the Resistor.
Hence, Resistance is a measure of the charge transport time!
*R ~ t*
Yet, in a real _ohmic_ resistor, temperature might increase with time, so the I-V slope changes, depending on the experimental procedure...
I just watch half the video and this channel is one of my favorits now
+netauri123, that's great to hear. Thanks. I am glad to be one of your favorite channels.
I love how unexpectedly philosophical this channel is. So much about the nature of intuition in general.
Thanks. I have an entire playlist titled "Physics and Philosophy" at the following link.
ua-cam.com/play/PLkyBCj4JhHt8Xoa58z9xTUz65egAd3zP1.html
MAF sensors in cars use this property of resistors to measure the volume of air passing through it. Excellent video. Keep up the good work!
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Thanks.
these videos are so coincidental because I just started my circuits class and it's like you make videos following the progression of my class :)
+Blackyisacat, I am glad that these videos are getting to you in time. In the past, I had a person complain that the video was on a topic that he had just taken his final exam in, and that if the video had been released just a few days earlier, it would have helped him correctly answer the question that he missed.
It only appears coincidental. Google knows everything. :-)
@@flumpyhumpy even till today
Thank you very much, your lessons makes things so crystal clear replacing memorization with real, deep understanding.
Not only are these videos perfect visual presentations, but the final thoughts of this particular video was almost existential. :)
Love your work, thanks.
Thanks.
My momma always said, "Life is like a box of resistors. You never know what you're gonna get."
Maybe she should've learned how to read resistor color codes.
Thank You for this video. People seem to think by solving the circuit is the same as understanding it, which is a fallacy that needs to be corrected. I've always was more interested in understanding a circuit & it's fundamentals which can be very hard to grasp because of how they describe it, for example, Ohm's law something you alluded to briefly in your video, you mention how it is not a actual law. Thank you for pointing that out.
What's presented here is a simplified _model_ of the V I circuit relationship. You can write a more accurate model that takes account of the many other factors, but this version is good approximation for most DC circuits. Temperature co-efficients are easily accounted for but AC circuits, and RF circuits in particular, are where things get trickier.
Exactly. It would be like arguing the existence of Newton's Second Law, and the Law of Universal Gravitation. Both laws are generalities of a larger picture. For instance, the Law of Universal Gravitation works for smaller objects, but does not accurately calculate the orbit of Mercury.
This is a very impressive animation that actually clear the doubts and expose the actual practical concept behind. Thank you for making such videos.
I really thank you. Your video is a simple and clear illustration of how voltage, resistance and current intensity interact. One can watch it OBSERVE, SEE how it works clearly. You are helping lots of people to really understand the basics of electricity. Thank you.
Ive spent hours upon hours trying to understand resistance and get an intuiative feel about how it worked and this video is the only one that got me to figure it out.
I am glad my video was helpful.
i have multiple accounts, and multiple times i would find your videos for mutiple reason. And, in all of those scenarios, i would like, subscribe and thank you. So here i am again: Thank you.
Everyone should thoroughly understand this tutorial before going any further.
A thank you.
Thanks.
Ohms law can be stated for puplis more correctly for many devices as " the resistance of a metal device of constant temperature remains constant". And resistor can be defined " a device for which Ohms law is valid". In the transation to greek language I made sime small changes in terminology to make video "compatible" with greek educational school system and definitions.
Original statement that Ohms law is NOT a law is at best MISLEADING and at worst plain WRONG! Ohms law established formula that Resistance R is proportional to the resistivity of the material (constant but different for given materials, such as copper, aluminum, gold, etc.) and the length of the wire and inversely proportional to the cross-section of the wire. That is the indeed the Law that Gerhard Ohm found. The reason why the resistance changes with temperature is precisely due to increase of the length of the wire with temperature increase resulting in proportional increase of the resistance. So, it is indeed a LAW even when you considered temperature effect! My daughter has made an experiment for sixth grade class of verifying Ohms Law by using different materials, like copper and aluminum wire and changing their length and measuring the current for a given DC voltage source to verify the above formula for Ohms Law. In fact, for magnetic circuits, Ohms law serves beautifully to introduce the equivalent dual concept, the Reluctance of the magnetic circuit as proportional to permittivity of the magnetic material, and the length of the magnetic core and inversely proportional to the cross section of the magnetic core. The AC inductance is then defined simply as turns squared times the reluctance! Dr. Slobodan Cuk (former Professor of Electrical Engineering at Caltech and inventor of Power Electronics switching converters).
See my videos on UA-cam.com/slobodancukTESLAco
The resistivity of a material is not constant, and that was my point. That is, even if you take the same length and width of the material, the total resistance may depend on temperature and a variety of other factors. It is just that for materials like aluminum and copper, this change is very small. But for the material used in thermistors, this change is very large, and this can't be explained in terms of the length or cross section of the material changing, but needs to be explained in terms of a change in the resistivity itself.
I understood the point about the controversy caused by the use of the word "law". Since my primary formation is as engineer, I am used to call it "Ohm's law", therefore in any mathematical relationship, a proportionality constant is used to fit the model to an "operational range". In this case, the R value is not really a constant that groups all the non-linear effects, moreover its definition only involves the V and I. For this reason, after the explanation of Eugene, I agree that it is not really a law, it is just a concept that works at a very basic level. Finally, it is importat to keep cuestionating all the knowledge, and also our own learning.
My high school teacher told us to think of resistance intuitively as of the amount of collisions that the electrons experience as they go through the wire, for example.: resistance increases with temperature because the atoms in the wire (or within the resistors) are vibrating more and thus are more likely to impede the path of the electrons; also the longer the resistor or the smaller its cross-sectional area, the more collisions. Is there any way to relate this approach to the existing definition of resistance as voltage/current ?
I have read somewhere that electric "flow" is dependent on the surface of the conductor and electricity spreads due to changes in the magnetic field surrounding the wire....
I, too, don't want to seem contrite, but I have to correct the claim of a logical fallacy on tried-and-true physics.
Ohm's law actually is a vector electro-magnetics equation. Since I can't write Vector notation here, assume that capital letters are vectors in the following, and I'll write out the Greek letters, and T is temperature.
J=sigma(T)*E where J is the current density, Sigma is the conductivity that is a function of temperature, and E is the electric field.
First thing to point out is that the conductivity of a material is temperature dependent, and that temperature dependence is taken into account in Ohm's law.
Second thing to point out is that the version of Ohm's law used in circuit analysis is a simplified scalar form, with a few important assumptions and simplifications.
That does not mean that the scalar form used in circuit analysis is incorrect.
Furthermore, just because one observes and minor inconsistency in a heavily simplified application of a physics edict does not mean that physics edict is incorrect.
The Feynmann lecture mentioned many times in the comments discusses that even the most fundamental laws are only approximations becouse reality never gets so simple as to be completly described by mathematical equations. On the other hand we have uncovered LAWs which are almost universal becouse they are approximations of some fundamental phenomenon underlying almost all physical phenomena. In my interpretation this video suggets that there is no such fundamentum behind Ohms Law. BTW I have read somewhere that electric "flow" is dependent on the surface of the conductor and electricity spreads due to changes in the magnetic field surrounding the wire.... Is it so? If yes - is there a YT animation on that?
thanks for Your comment...
I think you missed the point of Ohm's law.
The law doesn't say that the voltage divided by the current is the
resistance.
It states that: The current through a conductor between two points is
directly proportional to the voltage across the two points.
Now, the constant of proportionality is what we call the resistance.
.
In other words: Ohm's law states: V is directly proportional to I
Definition of the resistance is R=V/I
+Heliocentric I'd like to know what Eugene thinks about this, since what you say seems true.
+Heliocentric, but the current is not necessarily directly proportional to the voltage, and that was my point.
Physics Videos by Eugene Khutoryansky
This is already known.. Same as Hook's law (for example) is an approximation and is not applied in all cases to all elastic objects.
But your misunderstanding of the law is in your interpretation of the law as merely the definition of resistance..It is not that: as I said above.
So it is a "law" (limited .. I know !) and not a "definition" as you said in the video.
+Heliocentric I think the misunderstanding here about Ohm's law with respect to this video was that it is a physical principle or a concept that electromotive force (voltage in short no pun intended) pushes the current (which is the amperage) through a resistor or a device (resistance) across a circuit.
It is not the formula E = IR nor the direct and inverse proportionality of the 3 physical entities/information.
The confusion lies in the conflation of 'resistor' and 'resistance'. V = I • R is indeed true regardless of the resistor used and the condition it is in. The R represents resistance, not resistor.
1. There are preconditions to this law such as 'under constant temperature' which is to imply that the law would be talking about a simplified model of real life system like most laws in physics. Therefore, it is to be used more as a guideline rather than as a law beyond textbooks.
2. The statement is also not R=V/R. Ohm's law statement is that current flowing (the effect) is proportional to voltage (the cause) across the resistor. Resistance is only the constant of proportionality to represent the law as an equality.
Therefore, the law is not responsible for a variable resistance. Even under changing conditions (under the preconditions mentioned in 1), the law still holds.
I'm using these videos in my class, these videos are helping my students a lot.
Feeling fortunate enough to find such quality content on electrical engineering
I FINALLY GET IT WHY YOU NEED TO SUM ALL THE VOLATGE CREATED BY THE RESISTORS WHILE STACKED IN SERIES .
THANK YOU SO MUCHH
Glad my video was helpful. Thanks.
Came for Ohms law, left with a life lesson
V=I*R is not really Ohm's Law. V=I*R is how we define resistance, as you have clearly stated. A better formula for Ohm's law is dR/dV = 0 and dR/di = 0.
Ohm's law is that resistance is not a function of electrical operating conditions. Given a resistor of a material that doesn't change identity or geometry, that is maintained at a particular temperature by an independent system, its ratio of voltage to current is the same no matter what the voltage or current is. That is what Ohm's law is.
A more accurate way to explain that Ohm's law is not Universal is with negative resistance. This can occur in plasmas and electronic components where the current-voltage relation is highly nonlinear. See en.m.wikipedia.org/wiki/Negative_resistance
Eugene, the way you create your videos is genius. I always enjoy watching them.
Thanks.
At 3:15 I suggest the pink arrow of the voltage of the resistor to be pointing down only to indicate that it's voltage drop
You are right as this essentially is a DC circuit. The resistor upper terminal is positive and the lower one negative. Or the lecturer tried to draw the "counter vector" with same colour. In my ham radio training in the early 1980's the voltage drop was explained to be a counter vector of same size but opposite direction as the voltage measured accross the resistor. At that time they taught that the current flowing thru the load resistor gives rise to the voltage drop (counter vector) which has to be substracted from the battery voltage.
Ohm's law works fine for metals at low current densities. The temperature effect is a separate issue. Ohm's law des not work for non-metals, semimetals, semiconductors, electrolytes, gases or metals at high current densities. It has to be modified for alternating currents to take account of capacitive and inductive reactance. But for basic electrical engineering and electronics it is still a very useful formula.
I never said that it wasn't useful.
This is for the visual learners lol
I find it hard to believe that someone could learn these concepts easier by not seeing these diagrams. I know there are people who fair easier with audial or tactile stimulation when it comes to learning (or so it seems.) Let's say we take any person with all their senses intact and present to them these concepts in only one way: audial, tactile, or visual. It's hard for me to believe that someone could better learn about these physical phenomena with audial or tactile information but no visual. I'm not even that visual myself.
For instance, I listen to audiobooks a lot and most of the time, I don't paint a clear picture in my head about the stories or topics being presented (probably because I'm usually driving lol.) I can still understand what's being said and ponder upon it without visualization. Still, I find these visual presentations about physics to be far more helpful than just listening or just physically tinkering or rearranging.
I know I'm being biased about this but I would like to hear the perspective of someone who, if they only had one form of stimulation to choose from, would learn better with some stimulation other than visual.
Its more attractive tho
are you blind
I am just learning electricity new new.
so I don’t understand why to use resistors.???
Hi Eugene, during my studies in high school I would have needed these kind of representations of how electicity works.
Now, all thank to you, I can put images and representations on what I know of electricity, and it makes way more sense
+Pierre Leblanc, I am glad to hear that my videos helps make this subject make more sense. Thanks.
In programming, this would be called a leaky abstraction. It's an analogy that works most of the time, but "leaks" under certain circumstances.
Finally I came to know about Resistor ! Thanks for the video !
Thank you! I have been trying to make sense of this for years. A little closer. Love the ending.
Thanks.
so hold on. when the resistance changes as the resistor heats up, why does this change "ohms law" isnt that only changing one variable of the equation continuously, thereby changing the answer continuously? i dont know but doesnt it seem like ohms law is ever changing, along with the resistance?
Hence why the its Voltage/Current = Resistance and not Voltage/Current = Original resistor value. the clue is in the name, if the resistance alternates, more current flows, and the increase in current flow across it is proportional to the resistors deterioration. Therefore the law still applies :D
This is a lovely demonstration, but isn't ohms law " The PD of a metallic conductor is directly proportional to the current flowing through it, AT A CONSTANT TEMPERATURE"? So ohms law actually addresses the change in temp, which is why a filament bulb is a non ohmic device.
Is that PD the same for all metallic conductors? What does Ohms Law actually tell us about the phenomenas underlying the resistive force?
Ok so in any case anyone is still in the comments. Could someone clarify this for me?
What this video is impling is that: "Ohm law does not define resistance outside of it, therefore it's not a law". In the principal example of Newton's second Law, that even without (F=M*a)acceleration could still be defined in some way. The reason of not being a law is that the Resistance does not have a *constant* for the actual resistance, since it would decreasse with temperature.
So if in some way we define a constant for the *material* with the resistance at certain temperature; and another one for the *amount that it changes with temperature* and relate that through the current passing. Then it would be defined as a law? Like: *R = Constant - ValueOfChange*DiferenceInTemperature.* This way we could explain how the material change, and find a way to discover temperature by the new resistance.
I mean this is what we did with most atomic numbers. Found the value for a constant and related that with somethin. Molar mass and avogrados.
The Feynmann lecture mentioned many times in the comments states that even the most fundamental laws are only approximations becouse reality never gets so simple as to be completly described by mathematical equations. On the other hand we have uncovered laws which are universal becouse they are approximations of some fundamentum underlying almost all physical phenomena. In my interpretation this video tells that there is no such fundamentum behind Ohms Law. For example as far as I know there is no universally valid the "R = Constant - ValueOfChange* DiferenceInTemperature" equation. If there is such a constant valid for at least all electro-conductive metallic material than perhaps Ohms law would indicate some fundamental quality of those materials. I have forgotten a lot about physics so maybe such a constant exists :)
What a beauty! You seamlessly intertwined Life philosophy with Science at the end. You are THE BEST!😊
Thanks.
to have a meaningful existence a soul is like electron, it must pass many resistors and keep finding the return path even through the hardest resistance or jumping around various frequencies to make a complete journey in any given circuit (life time). That is the universal law.
Are you saying Ohm's Law isn't a law because ultimately is just a definition?
In that case, would Newton's second law of motion just be a definition of force and not a law?
+didles123, Newton's second law of motion does not suffer from this problem because "Force" is already defined independently of Newton's second law. For example, we have equations describing how forces are generated on charged particles due to electric and magnetic fields, and this is separate from Newton's laws. Newton's second law relates how this force that is generated will relate to the object's acceleration, and hence this is a statement about the external universe around us, and not merely a matter of semantics.
+Eugene Khutoryansky Although I have never heard it put as plainly before, I think your statement about Ohm's Law makes sense, and that distinguishing between it and Force = Mass times acceleration is being timid. I have heard it said that the force law mutually defines force and mass. We do not know what the property mass is except for the acceleration produced by some force. And we do not know what a force is except for the acceleration of some mass.
But in fact both equations slip something by our content detectors, while being definitions. Thus if we combine 7 (or whatever) equal masses and subject them to the same force as one mass, their acceleration is claimed to be one seventh. If we take 7 equal resistances in series and subject them to the same voltage as one, the current is claimed to by one seventh.
It is logically possible that 7 equal masses combined, and subjected to the same force as one, would accelerate differently than one seventh as much. We could just claim that the true mass was not found by adding, and figure the mass.
It is logically possible that 7 equal resistances in series subjected to the same voltage as one would conduct a current different than one seventh.
We could just claim that resistances did not add, and figure the resistance.
+binnacle true-north We have this apparent phenomenon in Newton's second law of motion as well. Externally applied force F is not always proportional to ma. This is always the work of an external retarding force (not accounted for in "your" simplistic calculation), but it does happen.
The dielectric field doesn't exist either (immaterial concept) but you're certainly not debunking that one.... hahahahahahahahaha
I guess that Eugene already posted a video about it.
Not convincing. R=V/I is not the definition of resistance. It is a physical law that relates those three properties of a system. Arguing that it isn't a fact of the universe because the resistance of a material doesn't stay constant is just ignorance of the more complex relationships involved.
The actual definition of resistance is R=resistivity •length/area. All three of those variables can be affected by temperature, and resistivity also depends on material composition.
I suppose you could try the same game by substituting the definition of resistance into Ohm's law:
r•L/A = V/I (here I am using r for resistivity) and then define resistivity as r = V•A/(L•I). But that doesn't stop resistivity from being a real property of a substance. The "definition" gives a way to measure resistivity.
In principle, at least, resistivity could be predicted from more fundamental physical theory.
Wow, very easy to understand these things explained things better than my instructors or teachers in college where they just read the books or what's inside the books in front without fully understanding the idea behide it and at the end we suffer. Thank you so much for making these kind of contents please continue doing
Thanks for the compliment about my videos.
It is a law. It's a law that tell us that current directly proportional to the voltage.
Johannes Sjolte Not an universal law.
Neither is Newton’s 2. Law
Johannes Sjolte I thought the same, but there is one difference. Both laws share the fact that you can define a new physical parameter, mass or resistance. But in Ohm's Law you have some materials that doesn't obey it, while in the other case every object has its mass remaining constant. But, that never happens actually, because of Special Relativity…
Therefore… Ohm's Law is fine, but has that particularity which other laws doesn't have.
Well said, "both with regards to science, and also with regards to life in general".
This video is worth thousand textbook pages. Also it is very enjoyable. I take my hat off to you.
Thanks. I am glad you liked my video.
There is always in everything we generally assume. We must assume for something to be right. That is generally speaking about language. Language is a memory we all share. We can have different understanding of words, we might associate words with each other, and we might have strong or weak feeling connected to words. Without knowing the meaning of words before hand we cannot use unknown words to communicate with others. Just like you does not understand other languages when spoken.
When it comes the subject of resistance: without further information and without giving it context. The formula of resistance is a simplified version of reality of resistance, in other word incorrect when it comes to accuracy.
We need to assume temperature is included when calculating voltage of material for the formula to be right.
Maybe we can get the right resistance with high accuracy if we take material purity of the conductor, absolute mass of material, absolute electron charge, molecular structure of the conductor, and take into consideration molecular structural change of the conductor during operation, then we can get more accurate resistance.
But we are not much interested to include all the measurements for general application. The formula of ohm is a workable formula for general use, but not for quantum purposes where nano accuracy is demanded.
Depending on demanded accuracy of calculation, the formula as it stands in my view does not qualify as a law. Since it does not include needed details to make it right and indisputable. It lacks information to make itself complete.
Feel free to correct me.
I summon thee Eugene of Physics Videos by Eugene Khutoryansky or anyone who can help :)
what about defining Resistance in terms of resistivity , length and Area. Now one would say resistivity is self defined But no we can also relate it to fundamental physical quantities like mass of an electron , charge of an electron , relaxation time and number charge density(no. of electrons per unit volume).
(further doubts) Isn't this the reason why Ohm's law specifically states that it's under constant temperature and physical conditions.
And I LOVE your videos , IT FEELS SO GOOD VISUALIZING EVERYTHING , thanks so much for all your efforts.(TOO GOOD)
Ohms law is very useful for circuit design and electronics so let's keep using it.
superb.. ..visulalizaton is ultimate.... Thq Eugene Khutoryansk.. really interesting
+avinash nani, Glad you liked it. Thanks.
Do I still go to jail if I break ohms law?
Yes you will be sentenced to the Event horizon of the Milky Way galaxy black hole.
@@raahimhadi4905 Sounds like a reward. That's how I'd want to go if I'm going to die anyways.
No, you just become a non-linear component, like a diode.
this was truely amazing :) thank you again for a lovely video.
+Men Skills, thanks for the compliment. I am glad you liked my video.
Your channel is great source to understand difficult concepts by esay way. Please make electrical machine related videos.
That's the reason why current is same in series circuit. The Resistors reduce the voltage and so, as I=V/R, so reduced voltage will automatically result in reduced current! As less potential difference will cause lesser attraction and slow the current down.
Some comments and facts: When Ohm did this finding, there was no knowlege of electron or inside of atoms. Ohm found out that resistance is constant for metallic coductors, mainly copper, iron. He knew that resistance depends on temperature. There was not found yet the law of conservation of energy. Many other things were not known. We use nowadays resistance for example radiation resistance of dipoleantenna is 70 ohms. It's a feature of space, not any wireconductor. Explanation for electrons movement in conductor is quite complicated. It would be interesting to animate this properly.
I was not aware of the history. Thanks for the information. I will add the movement of electrons in conductors to my list of topics for future videos. Thanks.
I am not sure the stated reason ohms law is not a law of the universe is important enough to not call it a law of the universe. Maybe Ohms law could reformulated and thus not fundamental, but derived from other laws. But, the video did not convince me of the distinction it was attempting to make. The argument sounded similar to arguing that acceleration is not a law of the universe because a rocket expels mass would have a changing acceleration. It seems to me that the flaw in this kind of argument is that both ohms law and newton's law were respectively for instantaneous values of resistance and acceleration, not if their values change over time with different inputs. If we accept F=Mass*acceleration is a fundamental law of the universe, then why cant we accept that Acceleration=Force/Mass is the same law, just stated another way. If im in a rocket one moment the force I feel changes over time because the mass in my rocket is changing. This distinction on changing over time is seems unimportant.
Besides, not all ohms are resistance that create heat. 10Vac supplied to a 1 om resistor will create 10 watts of heat as it allows 10 amps of current to flow. While 1 ohm of either Inductive or captive impedance will also limit current to 10 amps, but it does not loose any energy to heat, especially if the whole circuit is made of superconducting materials.
That argument is possible, and Feynman was worried he created definitions without proving their equivalence, and made an entire lecture about it: www.feynmanlectures.caltech.edu/I_12.html. Newton does really just define Force in the end, to be m*a. But showing equivalences such as F = GMm/r/r forces reality to behave in certain ways. Ohm's law is a property of most metals and is still at times inaccurate to degrees that can be felt. MOSFETs wildly disobey Ohm's law. LEDs disobey Ohm's Law quite notably due to heat. Op Amps also wildly disobey Ohm's law.
@@npip99 exactly what I was thinking!
the reason for increased current flow is because of ohms law , and the formula for resistors in parallel. remember that if you had a 10 a 20 a 30 and a 40 ohm resistors in parallel, the total resistance is always smaller than the smallest. In this case the total resistance being 4.807 ohms
By which software you make these kind of videos
Please reply
From india
I make my 3D animations with "Poser."
@@EugeneKhutoryansky
Thank you very much
Love from INDIA
Perfect ending!! Clap clap clap!!
Thank you Eugene.
+XtroTheArctic, thanks for the compliment about the ending. Glad you liked it.
Same! (Y)
considering ohms law came from observing electrical circuits, it seems to tell us something about the universe. I^2r certainly does and its by definition as well.
what a beautiful combination of Beethoven and physics
Thank you! Thank you! Thank you! This has been driving me nuts for days, but now I get it. Absolutely brilliant animations! ❤️💡❤️
Thanks. I am glad you liked my video.
"Having more resistors is like having a smaller resistance."
This choice of words illustrates exactly why I don't understand that splitting up the track increases the current.
Imagine being in a duel with swords. As long as the other person resists you sword attacks, you can't hit him. Hitting him really means getting through his blocking.
If the other person resists your attacks as strongly as you attack, you won't be able to hit him. But when you do hit him, you hit him once at one time.
In the above case, your opponent/resistance is really strong and you barely pass any hits.
In another case, you have three weak opponents who are not strong, so you can hit them much easier than it is to hit a strong blocker.
Similarly, the electricity that passes through three weak opponents (resistors) has an easier time getting through than the electricity that tries to get through a strong opponent (resistor).
@@excitedaboutlearning1639 The thing is, they're saying that 3 STRONG "opponents" is like having 1 WEAK "opponent".
I think the trick is that you can "attack" them all at the same time but it's still counter-intuitive.
What is the resistor I can use?
I absolutely love these videos, they are beautiful in presentation whilst perfectly coupled with simplicity in explanation ...I wish I had access to this material as an Apprentice Electrician 30 years ago. It would have sped up my theory learning curve significantly.
Amazing job....thank you
Thanks for the compliment about my videos.
These videos are so good. I wish I had known about them when I was in Physics II a few years ago.
Excellent video and very clear explanation, thank you so much!
Yes, thank you. Some straight answers for once. I don't know why there is all of this misinformation when learning things like this. I'll have to check out your other videos. Thanks again.
Thanks.
The video was great and the music was stimulating. Thanks for sharing. I'm definitely gaining confidence in this subject. I appreciate it!
Thanks. Glad you liked my video.
These transitions are blowing my mind.
Totally love your videos, they take something that may seem so abstract at first and turns it into a concrete and visual explanation that is incredibly helpful when studying physics. Thanks again!
Thanks. I am glad you like my videos.
What's your point exactly? As the resistance changes (due to temperature in this case), the current (or voltage) will adjust accordingly. Ohms law is not broken.
It's not a question about if Ohm's law works or not. It's about that it isn't law, it's the way that we define the resistence
That's like to say "The Gonzales law says that a velocity of any particule is equal to the space it goes divided by the time it took", but that is exactly the way we define the velocity.
If a dummy like me can through animations and slow concise explanation take on board these concepts in energy, then it's possible for anyone to understand and grasp what is being taught here in these videos. Bora Metin ( 2 comments below this one ) is correct. This is a revolution in education. Thank you. You have a new Subscriber.
Thanks. I am glad to have you as a subscriber.
@@EugeneKhutoryansky 😊
Great video, as always!! Thank you!
+Theenerd ジェームズ, Thanks. I am glad that you liked this one too.
How does Wats compare to ohms. How do you line watts up with ohms and get the best sound out of the speakers?
Thanks for the video! You obviously know a great deal so we must ask you why, oh why, the intrusive music? Best of luck!
Yeah it really didn't belong in a science video of this type. Otherwise it's a good video.
These animations are stunning! You make it easy to understand Ohm's Law. But personally, even at 2x speed, I find the video to be extremely slow. I guess that it makes these videos perfect for teachers in physics class, as they don't need to pause the animation during an explanation. Good work, keep it up :)
+Gabriel Cossette, thanks.
Many people think that V=IR is Ohm's law, but this equation is not Ohm's law. It's just the equation that defines "electrical resistance".
Liked it, why do I learn more from you than my teachers?? Lol
Douglas Chen don't learn from school if it's above primary/elementary level
Kira Vincent-Davis 😄
She's incredibly articulate, she does Anime voices also
School isnt effective at it's job, and it's job isnt desirable in the first place
I like your videos because it very difficult to visualise it ,now it is very easy and clear
Plz try to make physics videos in all topics of class 10
If ohms law is a definition.. Then newtons second law must also be a definition for term called force.. It will not define nature of universe but defines what is force.. So newtons 2nd law is also a definition.. Is it...
No, because we have definitions for the word "force" that are independent of Newton's second law. For examples, there are definitions that tell us how a force on a charged particle is created from electric and magnetic fields. Newton's second law then tells us how this force relates to mass and acceleration, for which we also already have independent definitions. By contrast, there is no independent definition for "resistance" (or "resistivity" / "conductivity"), other than ohm's law.
@@EugeneKhutoryansky thanks
Feynman would be proud. It takes a critical mind to notice that knowing the name of something is not the same as knowing something about the character of nature. We must always be careful to distinguish the two, especially when things get complicated in physics and there are so many names of things. Knowing the names helps you communicate, but it doesn't contribute to a true understanding of nature!
Almost everything we use is more complicated than we think. Unfortunately this video does a disservice to students in my opinion. It's implying that a fundamental equation used in electronics is wrong or invalid.
A truly fantastic and novel way to educate the youth. When I was a youth I struggle to understand electric circuit theory; oh how I wish teaching material such as this channel were available!
+Henderson Hood, thanks for the compliment.
Go ahead dears.I have learnt many new idea of current laws.May allah bless you.Carry on.
Thanks for creating such an animation vedios.
Glad my video was helpful. Thanks.
excellent video! could you tell me the name of the software you use to animate the images.
I make my 3D animations with "Poser." Thanks for the compliment.
Voltage is a bully. Voltage pushes the current around.
how are we able to figure out the temperature of the resistor by knowing the magnitude of resistance it provides?
This assumes that the relationship between the temperature and resistance is already known for that particular resistor.