# Homework Help: Faraday~ Induced Emf

1. Dec 9, 2005

### Kali8972

I'm reposting this because my homework is due in an hour and I still have not recieved help on how to solve this. I understand now that the the loop is equal to one. But could someone be generous enough to explain to me what the area is on problem 2 and 3 and why .503 is wrong for question 1?

I'm having a lot of trouble with the following questions. I was wondering if someone could steer me in the right direction and tell me what I'm doing wrong.

1. [GianPSE3 29.P.002.] A 20 cm diameter circular loop of wire lies in a plane perpendicular to a 0.80 T magnetic field. It is removed from the field in 0.10 s. What is the average induced emf?

2. [GianPSE3 29.P.005.] A 8.0 cm diameter loop of wire is initially oriented perpendicular to a 1.2 T magnetic field. It is rotated so that its plane is parallel to the field direction in 0.40 s. What is the average induced emf in the loop?

3. [GianPSE3 29.P.006.] A 7.6 cm diameter wire coil is initially oriented so that its plane is perpendicular to a magnetic field of 0.63 T pointing up. During the course of 0.12 s, the field is changed to one of 0.25T pointing down. What is the average induced emf in the coil?

Any help or suggestions would be greatly appreciated!! Thanks so much!!

Work:
http://www.pitt.edu/~slm17/problem1.jpg [Broken]
http://www.pitt.edu/~slm17/problem2.jpg [Broken]
http://www.pitt.edu/~slm17/problem3.jpg [Broken]

Last edited by a moderator: May 2, 2017
2. Dec 9, 2005

### emptymaximum

the radius is .2m, not .10
.10 is what you wrote for seconds.
the area of a circle is ╥r^2

a loop would be one turn
a coil would be multiple turns

Last edited: Dec 9, 2005
3. Dec 9, 2005

### Kali8972

Thanks!!! Stupid me haha! Got them all right now! Thanks!!