Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

  1. Jan 24, 2010 #1
    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. jcsd
  3. Jan 30, 2010 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    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).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook