Capacitors and Kirchhoff: Crash Course Physics #31
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- Опубліковано 2 гру 2024
- By now you know your way around a basic DC circuit. You’ve learned how to simplify circuits with resistors connected in series and parallel with a single battery source. But a lot of the real-world circuits that you encounter - and will have to describe - are much more complicated. For example, what happens when there are MULTIPLE batteries, connected in ‘parallel’? And what happens when we add ‘capacitors’ into the mix, with resistors in our DC circuits? On this, our last go-round inside a DC circuit, we’ll encounter junctions, loops, and capacitors!
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So, whilst I'm a huge physics nerd, I've never watched a single episode of CC Physics. I must say that the visual representation of the calculations are very nice. I love it; it's nice and clear.
Whoa, you took the words out of my mouth.
capacitors and capacitance have the capacity to incapacitate your flow of words
I'm incapable of repeating that capably.
Beyond my capacity... Oh! capability.
Always good to have a mixed flavor of physics and linguistics. 👍🤓
I just took an hour to properly watch this 10-minute lesson. But I actually like this format.
For those like me, who got confused how algebra part was done - this is how I did it:
First off, name all 3 parallel horizontal wires in this given circuit from top to bottom as i1, i2 and i3. Now, as Dr. Shini describes, apply Kirchhoff’s rule to loops found in the circuit. Let’s start with the equation for upper inner loop(loop 1):
Pick a starting point and a direction in which you are going to inspect the loop. In this case, they started at a junction next to 20V battery and went left in direction of current (conventional aka hole current) by adding resistor values both 5Ω and 40Ω to the equation #2 like this:
20V-5i2-40i1=0, where 20V is the battery, 5 is the value of the resistor in ohms and i2 is the name of a 2nd parallel wire where this resistor is located. Same applies to 40i1, that is 40 Ω resistor on the first wire. I continue in the reply of this comment below...
So how do we simplify this equation 2:
20V-5i2-40i1=0
-5i2-40i1=-20V
5i2+40i1=20V (multiply by -1 to get rid of minus sign)
0.125i2+i1=0.5A (divide everything by 40 Ω to simplify again. Also, this time, dividing 20V by 40 Ω, we put in use Ohm’s law where I=V/R, so 20/40=0.5A)
i1=0.5A-0.125i2
leave this equation for now, we can’t simplify it any more at this moment.
Let’s figure out equation 3 for the lower inner loop (loop 2) by starting at the same spot and going left and downwards:
20V-5i2+10V-15i3-25i3=0
30V-5i2-40i3=0
-5i2-40i3=-30V
5i2+40i3=30V (multiply by -1 to get rid of minus sign)
0.125i2+i3=0.75A (again, divide by 40 Ω and use Ohm’s law where appropriate)
i3=0.75A-0.125i2
Now equation 1. Remember, as shown in the video that i2=i1+i3, so we can now substitute i1 and i3 with our known values to calculate equation #1 like this:
i2=i1+i3
i2=0.5A-0.125i2+0.75A-0.125i2
i2=1.25A-0.25i2
i2+0.25i2=1.25A
1.25i2=1.25A
i2=A (1Amp)
So, substituting i2 in both previous equations we get this result:
i1=0.5A-0.125i2
i1=0.5A-0.125A
i1=0.375A
i3=0.75A-0.125A
i3=0.625A
@@martinsbeitans5179 You sir are amazing! Thank you!
I can follow this because i already understand this but i think it goes a little too fast for people who are trying to learn something new. The example with the loops was pretty advanced for a beginner and very briefly explained, just something to look at for next video, otherwise great series :)
Maybe you can answer this question, how did she derive that it was 1 amp flowing through L2 so that she could calculate the voltage drop for R2?
It seems you would have to know that before you can calculate voltage drop and current flow going through L1 or L2, so.the junction rule didn’t seem beneficial here.
This was the latest subject covered in school where I'm from. This timing is just too perfect.
dragon67849 I had a test on this literally 2 days before the video came out.... 😣
I'm really impressed with how well Kirchhoff's name was pronounced! Good job, Shini! =)
Great video! Currently reviewing for my Physics 2 exam.
I've heard enough "capacitor/capacitance" for a year now.
If you drink everytime she says "capacitor" you will be very hydrated #820
@Strawberry Dobreva That's not how drinking works, dude...
I've been struggling with this material in physics for two weeks now and this was so helpful wow
Could have used this video a week ago, might actually have passed my physics exam then lol
lol This is why I'm here today
@kylerobertm Just seen your comment now. Even with flopping that exam I managed to get into the university I had applied to and have since graduated with a Bachelor of Science. All ended well I suppose.
@kylerobertm Thank you! Appreciate the kind words. Your comment really made me reflect on the past 3-4 years. Hope you are well!
I literally make all the videos I watch with 1.5 and some times 2 speed but for these videos I can barely understand what shes saying
I still admit that these are some extremely useful videos that helped me alot
at 2:50 When talking in terms of current you never label it flowing negative to positive. current flow is always from positive to negative, whereas electron theory is negative to positive and is almost never used in real life. yes this is a physics course, but you're dealing with current, so label it as such.
I love the visuals you've used on this, but the workings out were done without explanation and lost track pretty quickly. I know the term crash course but I thought it would include the working out of the equations.
3:00 Does she mean the current direction is indicated as going from positive to the negative? That would make more sense to me. Then the orientation of the battery's is also going from positive to negative.
Where was this when I was taking circuits. Great video!
where did the A term come from at 4:22?
+Aniekan Umoren I believe they algebraically manipulated the first equation to solve for current one (I1) which gives I1=1/2I1-1/8I2. I think they may have rewritten 1/2I1 as 1/2A in an attempt to keep the equation from being confusing?
from Amp, like when you write a number en put J for joules.
When you take 20 Volt and divide it by 40 Ohm, you got a value in Amp, and in this case it's 1/2 Amp.
This is very easy to understand! Thank you for making educational videos such as this! May the team be blessed.
When teaching math, it's usually better to frame the exact problem first, and allow people to pause and work the problem out on their own. This allows those more ahead of the class to verify their confidence and it allows those behind to better understand their weakness. In this case you didn't reveal all the resistor values until you told us the answer to the problem. Telling us the answer first is less motivating, backwards teaching.
I get what u mean :) but you can only work out a problem after u understand the concept... and for most ppl watching it is the first time coming across problems like these
1- I love you
2- I think you should've talked more about analysis methods like nodal and mesh and circuit theorems before moving to Magnetism, still really great videos
Abdalrahman arrob In my opinion, circuit theorems are for advanced electrical engineering, so for a short and simple crash course video, it will be too much to include. Furthermore, Kirchoff's Voltage and Current Law already serves the basic of nodal and mesh analysis, and she did explain both of them, just with the term "junction and loop rule". It is basically nodal and mesh analysis.
This isn't impossible to follow. But, without jokes, more character animation for samples (like seeing the spark go driving down the current like it's driving a car), and at this fast speed of information absorption, it's a rough go. I just want this to be more fun to watch Nothing at all against the host, would love her on something a little more light hearted, or just another go at a few of these episodes, maybe with a longer run time for breathing.
Also, I am aware Hank is jumping on top of things to make sure all future content is equally produced. I appreciate this channeled ability to address itself and audience.
Thank god for this video, my physics teacher doesn't teach or explain anything to us and just gives us random worksheets to do and expects us to know things aosfasldfadfadf
2:00 OMG I just realized that's a Roller Coaster Tycoon reference, after rewatching the part a few times to understand the concept xD Park guests trapped on an island surrounded by water in a square grid lol, how did I miss that at first?
At time 4:49, how come V4 turns into I3R4 and then into 25I3? Wouldn't V4 equal I4R4, which is 25ohmI4?
nvm sorry! i forgot they have the same current since they are in series
Thanks Doc Shini. I appreciate the time. Cheers, Bobby :)
How is the third loop actually a loop? They're flowing in opposite directions - a charged particle couldn't flow through it and arrive back at the same point.
A loop need only be any physical loop. If the direction of the current if opposite in half the loop, you just add a negative sign to your IR terms.
Nice lesson but it was fast and furious that I had to go all over again.
These videos are saving my life and grade
*currently cramming for a science olympiads competition next week*
4:20 Equation 2 comes out of nowhere. Not sure what the 1/2A and the 1/8I means.
Its the same as the previous equation (0=20V-I2R2-I1R1), just using the values of R1 and R2, and some algebra.
Thanks a lot. I tried some algebra and it worked just fine.
0 = 20 V - I2 * 5 Ohm - I1 * 40 Ohm
I2 * 5 Ohm + I1 * 40 Ohm = 20 V
divide everything by 40 Ohm
I2 * 5 Ohm / 40 Ohm + I1 = 20 V / 40 Ohm
I2 * 0,125 Ohm + I1 = 20 V / 40 Ohm
I2 * (1/8) Ohm + I1 = 20 V / 40 Ohm
because I = U/R
I = 20 V / 40 Ohm = 1/2 A
I2 * (1/8) Ohm + I1 = 1/2 A
I1 = 1/2 A - I2 * (1/8) Ohm
Thanks, that helped.
A little fault was: when you divide by 40 Ohms it is I2 * 0.125, not I2 * 0.125 Ohms. So here is the corrected version for other viewers, who confused that:
0 = 20 V - I2 * 5 Ohm - I1 * 40 Ohm
I2 * 5 Ohm + I1 * 40 Ohm = 20 V
divide everything by 40 Ohm
I2 * 5 Ohm / 40 Ohm + I1 = 20 V / 40 Ohm
I2 * 0,125 + I1 = 20 V / 40 Ohm
I2 * (1/8) + I1 = 20 V / 40 Ohm
because I = U/R
I = 20 V / 40 Ohm = 1/2 A
I2 * (1/8) + I1 = 1/2 A
I1 = 1/2 A - I2 * (1/8)
Capacitor's, capacitors, capacitance.
New seson of Crash course history is what we need...!!!
sweet, and I can't wait till we get to how quantum mechanics shapes our consciousness and connects us to the energy of the galactic center!
That picture of the old folks that Crash course loves so much has gotten into the title screen.
This makes it way harder than it really is
isn't it supposed to be 25*I_4 for the last term in equation for loop 2 at 4:50 ?
She explains everything so effectively
Your German pronounciation is really good
crash course music theory?
I need that
Please make the uploads faster, so i can keep skipping my lectures... God bless!
How did you get the equations? Like for equation 3, you have 30V - 5I2 - 40I3 = 0. I mean this in no offense to the video but I have no idea where you got this from.
When you had the diagram for capacitors in series, your charges were backward. Also, in terms of a diagram, charges are meant to flow from positive to negative. They actually flow from negative to positive but that is not how they are diagramed.
Shouldn’t the current of the battery go from positive to negative? I just know that the bigger bar on the battery is positive and negative is the smaller bar and you want to go from bigger bar - loop - smaller bar.
for the current direction, at 3:06 she says that it travels from negative to positive...isnt that incorrect?
yup it's incorrect for the current direction. The electron flow is from negative to positive, and the conventional current is from positive to negative ( which is technically the opposite direction of the real current which is the electron flow ). She should be refering to the direction of conventional current in the video.
This is so interesting. Thank you!
I am unable to understand at 4:19 step some one help me please.
If I hear the words "capacitors" and "capacitance" any more, my head just may explode.
where did you pull that 1/2 amp in the equation 2 (for example) from?
+Simon Cajagi I believe they algebraically manipulated the first equation to solve for current one (I1) which gives I1=1/2I1-1/8I2. I think they may have rewritten 1/2I1 as 1/2A in an attempt to keep the equation from being confusing?
Sirdragonx Rocks this attempt made it even more confusing 😑😑😑
hey! late answer but I think it´s because of the values of the resistors.
In the circuit we have resistor 1 (40 Ohms) and resistor 2 (5 Ohms).
because of Ohm's law, to find the voltage, we multiply the resistance times the current, so:
R1*i1 + R2*i2 = 20 ampéres (the voltage of the battery)
if we substitute the value of R1 and R2 for it's values, we have:
40i1 + 5i2 = 20A
If we move 5i2 to the other side:
40i1 = 20A - 5i2
If we divide all the values for 40, we have:
i1 = 20/40A - 5/40i2
i1 = 1/2A - 1/8i2
I hope I've helped!
(btw english isn't my native language, so excuse me if there's some grammar mistakes)
@@mellandrade1364 Thank you! Thank you!! THANK YOU!!! The A was totally throwing me off!
I'm not sure this question has been covered in previous episodes or has anything to do with this particular topic, but would you be able to answer how theoretically a space craft traveling outside our galaxy could continue it's journey without any need for fuel? (gravity is irrelevant, I've already tried) Thankyou!
False alarm, I found my answer. It was newton's first law, an object remains at rest until an outside force acts on it
Oh cool. Just found out I can solve this with a matrix. nice nice
All I hear in the second half is capaci... capaci... capaci.... Nice presentation of Kirchhoff's Laws. Thank you.
1:44 me every time I study stuff
4:20 Where did this equation come from? I fear you didn't really explain it in the video :/
here V3=9.375volt, V4=15,625volt
Where did the fraction come from?
For those first current loops, I would have just used Superposition
I've been able to follow the last 2 or 3 episodes which was a joy but i still don't understand capacitors and capacitance yet, unfortunately.
"kirkhoff's loop rule" 3:28
thank you!
So current flows into, a capacitor, and an exactly equal current flows out, but, zero, current flows through, What about charge: Is charge a number of neutral particles, or a number of charged, particles, and of the latter is not their charge field, flowing through, momentarily...
why was this reuploaded I watched it this morning
Error in an equation.
THANK YOU. THANK YOU. THANK. YOU.
Thanks 👍
Are the signs in "equation 2"? cause if you moved 20v over to the left making -20v and then divided by -20V you would get .5 A+.125 I not .5 A -.125 I
are the signs in "equation 2" wrong*?
when does the direction of the current in the resistance change to negative, mam?
They messed up with the current directions, their diagram shows current flowing from the positive to the negative terminal but she said the opposite. Excellent video otherwise, as always
Why wasn't this uploaded when I was in school? :D I have a feeling some books tend to neglect a few explanations and examples.
Yeah, was pretty sure you guys already uploaded this one. I made a Kirchhoff comment, about logic and everything. :/
You'll want to make the comment again. It's gone away.
hi CrashCourse
Lest time I came this early
I spelled last correctly
Jordan Pinkston ok dad
Jordan Pinkston wat 😁
Jordan Pinkston You mean premature ejaculation?
😂😂😂
please can u do a vid on gravitational potential energy?
You did an American commercial there at the end... I thought you were British!!! Lol!
Crash Course, please where is the Arabic captions??? please I want it. I can't make the most of this video if there is not my language captioned. please do it for me in the shortest time and thank you
Big fan of the Rollercoaster Tycoon 2 joke in the rollercoaster analogy with the people trapped by the water
Can you do a video about magnetic fields?
I yam totally kapassified .
Nevermind the people that complain about the video being too fast. If they have trouble following they can watch it in 0.75 or 0.5 speed. This works perfectly if you have any clue at ALL about the words being used. In this video, all you need to know is the difference between capacitor and capacitance. That's pretty much the only real confusion that can occur..
Nice video but whats going on at 3.45 ??
*Pro tip: set the playback speed at 0.75x*
kifuuu?
or
kirchhoff?
How did you make equation 2 and 3?
y'all i've been watching these videos on the speed of 0.75, you can change the settings in the video. she speaks slower there, and you can understand everything she says without getting info overload.
so many capacitanceeeeeeee wordss!!!!
If I had a dollar each time she says capacitors or capacitance, I'd be a millionaire now.
how did he get the 0.375A At 5:47 please explain it to me Im confused
CrashCourse there should be episodes for civil and mechanical engineering concepts since physics had basically become electrical
It seems ridiculous to me that she's speaking so fast when this is clearly an educational video. I've had to pause and rewind several times just to wrap my head around all the information!
lol watch at 0.5 speed :D
that's...why they put it on youtube. that's also why they have closed captions on every video!
crash courses are for those that have never taking a certain course and want he jest.
That's why it's called "crash curse".Try reading theory before watching it if you can't keep up...
It's a crash course. I'm using it as a review, and because there is a lot to cover for the midterm, I am watching all of these video's at 1.5x speed.
This is, indeed, getting complicated.
guys you can speed up the video to 2 times for about 30 seconds and when you switch it back to normal its 100000 times easier to unerstand ( in case you guys think its going too fast )
I could not find a corroboration online for your "silent R" pronunciation of "Kirchhoff" in either German or English. The R was present in all sources (even if slightly audible).
As a German native speaker I can confirm this pronunciation is very close to the original. Most varieties of German (including the standard variety) are non-rhotic, that means, in certain settings (including this one) an "r" is reduced to a "near-open central vowel" (IPA symbol ɐ) which, as a reduced vowel, is more often than not pronounced with less intensity than a regular vowel. Listen closely and you will hear the "i" gliding into a much weaker "ah" sound which is just the way most German speakers would pronounce the name. (But bear in mind: as with most major languages, there are a lot of different dialects in German, and especially in the south you're much more likely to hear people pronounce "Kirchhoff" with a clearly audible rolled "r".)
Logan Graves being Austrian (same as German really), I can actually hear the r 😅
DAMN !!
too fast video
Crash course dude... That's expected
Oh two years too late... Sorry
PSA the intro is full of puns
i'm so desperate i'm watching a crash course video in 2x speed :((((((((((( exam's in an hour
I am Kirchhoff's great great great great etc. nephew.
Nice fig
Shift the speed from normal to
x.75
what does A equal?
nvm, its amp
the video is too fast, same with a lot of these type of videos
Zuhayr not zuzu neither is good
its called pause woaaahh
change the speed of the video to 0.75 in the settings, that's what I do with all of their videos
Really? I watch it at 2x speed for cramming. Extremely dense and effective.
it's a crash course and it delivers, not as a means of learning--but as fast review