# Power factor

Discussion in 'Homework Help' started by kvi037, May 17, 2013.

1. ### kvi037 Thread Starter New Member

May 17, 2013
17
0
Hi,

I'm struggling with this task for my preperation for a exam next week.

An AC voltage of amplitude 150 volts is impressed across a pure resistance of 100 ohms. Calculate the current and the power dissipation when the frequency of the voltage is 60 cycles/sec.

2. ### MrChips Moderator

Oct 2, 2009
17,750
5,542
Firstly, we have to make some assumptions.
When you say amplitude we would assume that to be the value A as in v = Asin(ωt).

To calculate power, we need to use the rms value.

The power factor is 1.

screen1988 likes this.
3. ### WBahn Moderator

Mar 31, 2012
23,565
7,212
The thread title implies that you are looking for the rms values, but the question sounds like you might be looking for instantaneous current and power dissipation. Could you please clarify?

4. ### WBahn Moderator

Mar 31, 2012
23,565
7,212
Basically correct, but your equation is not consistent with your result.

You have

I = 150/0.707*100, which is 21216

You you should get in the habits of tracking your units throughout your work. So it should be:

I = Vrms/R = (150Vpk)*(0.707Vrms/Vpk)/(100Ω)
I = 1.0605 Vrms/Ω = 1.061Arms

5. ### kvi037 Thread Starter New Member

May 17, 2013
17
0
Sorry, I just wrote the calculation in a wrong way.

Thanks for that you wrote it in the correct way