# Homework Help: Help me plez

1. Apr 23, 2009

### samalafaee

Help me plez!!!!!!!!!!!!!!!!!

I am a student. can anyone help me and solve the following problem:

The current through a capacitor is given by i (t) = 7 sin π t mA. If the energy stored at t = 200 ms is 3 μJ, what is the value of the capacitance?

which formula I have to use?

plez , I will wait ur help!!!!!!!!!!

2. Apr 23, 2009

### Staff: Mentor

Re: Help me plez!!!!!!!!!!!!!!!!!

Welcome to the PF. You must show us the relevant equations, and you must show us your attempt at a solution, before we can offer any tutorial hints. That's part of the PF Rules (see the link at the top of the page).

Show us the relevant equations and your attempt at a solution please....

3. Apr 23, 2009

### samalafaee

Re: Help me plez!!!!!!!!!!!!!!!!!

the relevant equations:
i(t)= C dv/dt
Energy stored: w(t) = 1/2 CV^2

attempt at a solution:
I am not sure about my attempt , I am confused because I don`t know from where I start.I tried to use integration to get C......!I just need the first step