# Homework Help: The current in the circuit ?

1. Dec 21, 2009

### Fazza3_uae

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 = $$\sqrt{}2$$ * 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. Dec 21, 2009

### willem2

Re: The current in the circuit ...??

17 W is the average power over a full cycle. It's equal to $I_{rms} V_{rms}$. You used this value as if it was the instantaneous power at t=0.25T