# Capacitance Current and Power

1. Sep 30, 2013

### k_squared

1. The problem statement, all variables and given/known data

The voltage across a capacitor with a value of 0.01 Farads is v(t) 100*cos(2pi60t). Find i(t),p(t),and w(t).

2. Relevant equations

i(t)=Cv'(t) [current]
p(t)=i(t)v(t) [power]
w= integral of p(t) [Energy stored over time]

3. The attempt at a solution

I was able to correctly determine the current of capacitance, -120*pi*sin(2pi60t) Amperes. However, this multiplied by the voltage, does NOT equal the given answer of -18,850sin(2pi120t) Watts.

Could someone please clear this up for me? I would've used proper symbols, but the test is quite shortly, no time to mess with that ... :/

Thanks!

2. Sep 30, 2013

### phyzguy

Try using a trig identity for Sin(2X).