1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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

    Redbelly98

    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