# Homework Help: Find out the charge is delivered to the element and power and energy?

1. Jan 24, 2010

### sonutulsiani

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

Current flowing through an element is i(t)= 2e^(-t) and voltage across that conductor is v(t)= 2 (di/dt). Find out the charge is delivered to the element and power and energy consumed by the element in between 0 to 3 seconds.

2. Relevant equations

i(t) = dq/dt
power = v * i
Energy = power * time

3. The attempt at a solution

I got charge,q = 1.9 C

For power, I got voltage as -4 e^(-t), multiplying it with current, and I got Power as -8 e^(-t) but i must be getting the answer in some number right?

And what about energy? I don't have power till now, so couldn't calculate it.

2. Jan 30, 2010

### Redbelly98

Staff Emeritus
I agree.
No, your expression is correct. Question for you: if the power consumed is negative, what does that imply?

Power consumed is dE/dt, where E is the energy being consumed.
The equation you had, "Energy = power * time", is only true if the power is a constant value (it isn't constant in this problem).