# Really basic question about ac circuits

Discussion in 'Homework Help' started by wannabedoc123, Dec 4, 2010.

1. ### wannabedoc123 Thread Starter New Member

Dec 4, 2010
2
0
Hey this is pretty simple but I'm just not getting it. I'm sorry if I sound really dumb, but I have the following questions:

1. What exactly is power factor? If the question says the power dissipated is 25% of the power supplied, what do we take the power factor to be? 0.25? And if it says that the power consumed is 25% then?

2. if a bar magnet falls freely vertically and passes through a copper ring in its path; but the ring is cut (ie it has a gap), then will emf be induced in the coil?

I'd really appreciate any help anyone could give me!

2. ### jimmychacha New Member

Dec 1, 2010
10
1
Doc, I can help you with number two, as I am currently studying this subject in Physics. An EMF, or voltage potential will be induced at the two ends of the copper ring. This emf will probably be very small since the "ring" you describe sounds like one coil, or turn of copper. If the ring were made of multiple turns, the emf would be greater. Also, the emf will last only a short period of time, the time that the magnet is in motion through the ring. When the magnet stops, the emf is gone. The faster the magnet moves through the ring, the greater the emf induced. When the magnet is withdrawn from the ring, an emf of opposite polarity is induced.
Hope this helps,
Jim

Nov 25, 2009
5,142
1,266
4. ### mik3 Senior Member

Feb 4, 2008
4,846
63
I think you have confused power factor with efficiency.

Can you show us where did you find these questions?

5. ### blah2222 Well-Known Member

May 3, 2010
554
33
Like what was said before, you have mixed up efficiency with power factor.

Power Efficiency = Pin/Pout

Power Factor = Pout/|S|out

Where |S|out is the apparent power dissipated from the load.

Hope that helped.

6. ### wannabedoc123 Thread Starter New Member

Dec 4, 2010
2
0
Thank you so much, everybody!