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How to calculate Ic without using ohm's law?

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dr.power

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HI there,

I have a 100n Capacitor in series with a 1K resistor connected to a function sine generator at 1KHz. I used 2 channels of my scope to see the voltages and waveforms acroos the cap and the resistor. I know how to calculate the current going through the circuit by ohm's law but I am not sure how to do it by this formula:
Ic= c dV/dt
Since the input voltage (coming from function generator) is sinusoidal then the voltage across the cap is cosine. I am able to see the waveforms and their value by my digital scope but not sure how to calculate Ic (actually I do not know what to do with dV/dt). I think dV/dt will be equal to coswt but I can not go ahead....
Please help

Thanks
 
dV/dt is usually used just to calculate the voltage or current on a cap with step type DC input changes. Using the differential dV/dt to calculate the current in an AC circuit involves some differential calculus calculations which tends to be messy. Much easier is to calculate the impedance of the circuit and the current using AC circuit analysis.
 
dr.power,

The formula you mentioned will certainly give you the instantaeous current. Is that what you want, or do you want the average, RMS, or peak current? Why are you reluctant to use the impedance formula I = V/Z to find the current? And don't forget the series resistance.

Since the input voltage (coming from function generator) is sinusoidal then the voltage across the cap is cosine.

A cosine voltage/current is also sinusoidal. A sin and cos wave of equal amplitude differ only in their relative phase with other.

Ratch
 
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