# Homework Help: One more question

1. Feb 14, 2006

### tj03

I have worked my way through this question, and I still get a wronge answer.

A piece of copper wire is formed into a single circular loop of radius 9 cm. A magnetic field is oriented parallel to the normal to the loop, and it increases from 0 to 0.70 T in a time of 0.45 s. The wire has a resistance per unit length of 3.3 10-2 /m. What is the average electrical energy dissipated in the resistance of the wire.
r= 9cm= .09m
change in t= .45s
B= .70T
restitance per unit length= 3.3 x 10^-2
N= 1
emf=-80.15
mag flux 178.12

I figured R to = .01866
I = 4295.25
P= -344264.29 (I *EMF)
E= 344264.633 (pt)

anyone know where I went wrong?

2. Feb 14, 2006

### Staff: Mentor

Couple suggestions -- First, carry units through in all your calculations. It will help you to avoid mistakes, and will help us to read your calcs a lot easier (at least for me). Second, the power will not be negative, and it woun't be 3244264 in any reasonable units. You also probably won't get an emf of 80V with a single turn and that slow ramp rate.

Show us which equations you are trying to use, and show all your units so we can help you if you still don't get it.

3. Feb 14, 2006

### Astronuc

Staff Emeritus
How did you calculate the emf?

What is the relationship between emf and the changing rate of the magnetic flux, and the magnetic flux and magnetic field strength?

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