# Homework Help: Electromagnetic Induction and Waves

1. Jul 2, 2009

### jlmessick88

1. The problem statement, all variables and given/known data
The figure shows a 10-cm-diameter loop in three different magnetic fields. The loop's resistance is 0.10 ohm.

http://i63.photobucket.com/albums/h148/jlmessick88/jfk_Figure_P25_12.jpg

For case (a), what is the induced emf?
ε = mV

For case (a), what is the induced current?
I = mA

For case (a), what is the direction of the current?
clockwise
counterclockwise
no current

2. Relevant equations

ε = |ΔΦ/Δt|
Εcoil = N * |ΔΦpercoil /Δt|

3. The attempt at a solution
No idea :(
Any....ANY help would be great!
Thanks!

2. Jul 2, 2009

### cepheid

Staff Emeritus
You've given an equation for the induced emf in terms of the change of "Phi" with time. What physical quantity is Phi? Based on the answer to that question, how would you compute it?

3. Jul 2, 2009

### jlmessick88

that's where i was getting confused...i wasn't sure if there was some way i could solve for "phi" given the info...
if that's not the correct equation then where do i begin??!?

4. Jul 2, 2009

### cepheid

Staff Emeritus
I didn't say it wasn't the correct equation.

There is a way for you to solve for Φ using the given information. If you knew what Φ was, then you would have known that. So, answer my first question first please. What is Φ?

5. Jul 2, 2009

### jlmessick88

well i couldn't used the equation Φ= ABcos() b/c i don't have a magnetic field...
i couldn't use ε = |ΔΦ/Δt| b/c even if i made it become ε = pi * r^2 |ΔB/Δt| b/c i still don't have a magnetic field

6. Jul 2, 2009

### cepheid

Staff Emeritus
What you mean you don't have a magnetic field? A magnetic field is depicted in each of the three diagrams, and its rate of change is given.

7. Jul 2, 2009

### jlmessick88

oh!!! ok...so ...for the change in magnetic field and time, i would just create the change over some period of time determined by myself correct??

8. Jul 2, 2009

### cepheid

Staff Emeritus
Not really necessary. The rate of change for the leftmost case is given as half a tesla per second

So you know that if the time interval (change in elapsed time) is 1 s, then the change in magnetic field will be +0.5 T.

Can you see that this is a way of saying (in words) that:

ΔB = 0.5 T

Δt = 1 s