AC voltage across a capacitor (derivation) | Alternating currents | Physics | Khan Academy
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- Опубліковано 4 сер 2024
- When an alternating voltage is applied across a capacitor, the current leads the voltage by a phase angle of 90 degrees. This means the current oscillates a quarter of the cycle ahead of the voltage. Let's derive an expression for this current.
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I have question please : i am confused how we can write : Vs= Vc knowing that the capacitor "gradualy" raise its voltage and doesnt respond instantaneously with the voltage source ! , why we are ignoring this fact and treating capacitor as if it is a resistor ?
Thank you in advance
Thanks for your effort!
I have a question: how is it possible in initial moment of time when V=0, I=max? In this point voltage difference is zero, so the capacitor wouldn't "know" how great it would be to "calculate" I max. Really really looking forward for your answer, thanks.
Capacitor is a device for storing electrical energy . My point is when voltage [ potential difference ] is zero the potential difference in the whole circuit is same which is v = 0 this can only happen if the Capacitor is charged to its extent and at the very stage to get discharged. Hence it holds the maximum current
You shouldn't look at magnitude of voltage but rather how fast the voltage of capacitor is changing because current of capacitor is dependent on how fast the voltage is changing. You have equation ic = C * dv/dt which tells you that current is at maximum when voltage is changing the fastest (when the line on graph is the sharpest which happens across 0V). Because if you want faster change in voltage you need more current = more charge. When voltage is at maximum current is at 0 because at that point voltage doesn't rise anymore and the change in voltage is 0. It's quite logical if you think about it.
Plz explain with numbers.
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How does alternating current arise the applied voltage equal to the voltage inside the coil and opposite in direction? And why
How does alternating current arise when the applied voltage is equal in magnitude to the voltage inside the coil and opposite in direction?!
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If voltage across capacitor is same as voltage generated then how the current would flow ???
No you have to look at it other way. The voltage source creates current that charges capacitor to the voltage of the source. But voltage of source is constantly changing which means that capacitor must be also constantly charging and discharging with current. You would be correct if we were talking about DC circuits because in DC circuits capacitor charges to source voltage and then there is no more current because voltage isn't changing like in AC.
Why we change the function from sin to cos?????
Differentiate kiya hai
Sin ka differentiation cos hota hai
Sir please hindi me padhya kijiye
In the graph the peak value of current is shown greater than that of voltage is this correct?
You can't compare voltage and current on the graph by their height because they are measured in different units. Current is measured in Ampers and voltage is measured in Volts. You could have voltage bigger than current if you choosed so.
Why voltage is lesser than current ?
You can't compare voltage and current on the graph by their height because they are measured in different units. Current is measured in Ampers and voltage is measured in Volts. You could have voltage bigger than current if you choosed so.
I don't still understand
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Thank you for your great educational lessons
I have question please : i am confused how we can write : Vs = Vc knowing that the capacitor "gradualy" raise its voltage and doesnt respond instantaneously with the voltage source ! , why we are ignoring this fact and treating capacitor as if it is a resistor ?
Thank you in advance
In video he put capacitor directly across source which means that the voltage of source must be equal to voltage of capacitor. The current adjusts itself so that this can happen. When voltages is changing the fastest (the sharpest line is across 0) the current is at it's maximum and when voltage isn't changing the current is 0A. It's because of the equation: ic=C*dv/dt which tells you that current is at maximum when voltage across capacitor changes the fastest.