# Phase Differences in of voltage in RC and LR circuits

1. Aug 30, 2014

Hey guys can someone please give me a good explanation on why in an RC circuit the resistor voltage is leading the capacitor voltage by 90°. While in an LC circuit the resistor voltage is lagging the inductor voltage by 90°.
Thanks

2. Aug 30, 2014

You are talking about an AC circuit where the voltage is given by the equation V= V0sinωt. (ω= Angular frequency). Represent the current in similar terms and derive respective equations for a purely resistive, purely inductive and purely capacitive circuits. Then compare the phase difference.

Hint: CosΘ and SinΘ has a phase difference of 90 degrees.

3. Aug 30, 2014

hmm do you think you could explain it to me in physical terms, cos mathematically seems really confusing

4. Aug 30, 2014

Do you want me to explain you the concept behind alternating circuits?

5. Aug 30, 2014

I understand the basics of AC, and the concept of reactance, and what a capacitor does and what an inductor does to AC current i just dont get why one leads the other

6. Aug 30, 2014

### gsal

Hhhhmmm...I am not sure I can leave math out of the question and explain in pure english...

The way I see it, in a capacitor, voltage is directly proportional to charge and charge is the accumulation (integral) of current; so, voltage is proportional to the integral of current.

In an inductor, voltage is produce only when the current changes, i.e., voltage is proportional to the derivative of the current.

Without bringing explicit equations into the mix...does this help?