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: The current in the circuit ?

  1. Dec 21, 2009 #1
    The current in the circuit ...??

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

    An AC voltage of the form V = Vmax sin 2*pi*f*t , with frequency 22 Hz and maximum voltage 763 V, is applied across a 17 W light bulb. When the voltage is first applied.

    a) what is the current through the circuit?

    Three Choices :

    1. the maximum current
    2. 0
    3. the rms current

    What is the correct answer and why ... ??

    b) When t = T/4 , where T is the period of the applied voltage, what is the current in the circuit?

    2. Relevant equations

    P = I * V
    I max = [tex]\sqrt{}2[/tex] * I rms
    T = 1/f

    3. The attempt at a solution

    In part a) i think that when the voltage is first applied means that time is ZERO so it could be ZERO the options # 2

    In part b) I substituted t = 0.25T or 0.25/f in this formual

    V = Vmax sin 2*pi*f*t

    I found V then I used P = I * V and solved for I but i got wrong answer.
  2. jcsd
  3. Dec 21, 2009 #2
    Re: The current in the circuit ...??

    17 W is the average power over a full cycle. It's equal to [itex] I_{rms} V_{rms} [/itex]. You used this value as if it was the instantaneous power at t=0.25T
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook