# Magnetic Force,EMF, Flux question

1. Mar 14, 2006

### nophun6

I have three questions that I think I have the answers to, but would like someone to tell me if I did them correctly. Thanks!
Q1. Given B= 0.8T, a coil with 1 loop with length of 20cm, a current of 5.0A, what are the size and direction of the magnetic force on the loop?
A1. Would I just use Fm= IxBxL = (5A)(.8T)(.2m) = .8 N ???
As for the direction I know it involves the right hand rule, and the current moves to the right, so would the magnetic force be pointing up ?

Q2. What is the magnetic flux through the loop?
A2. Would I use: Flux= ABcos0 = pi(.2)^2 (.8T) (cos0) = .101 Wb ??

Q3. If the magnetic field has a cut off at the top of the loop, and the loop is pulled completely out of the field upwards at v = .2 m/s:
what EMF would be generated and if the resistance was 4 ohms, what would the current be?
A3: EMF= Blv = (.8T)(.2m)(.2m/s) = .032V
O = EMF/R = .032V / 4 ohms = .008A

do these look right? thanks.

2. Mar 14, 2006

### nrqed

You have to tell us in what direction the B field is pointing!!! (with respect to the normal of the loop, let's say)

3. Mar 14, 2006

### nrqed

Oh wait, it's a *square* loop (when I saw your solution I thought you had in mind a circular loop!). Then it's ok to square the length of one side, but there shoul dbe no factor of $\pi$ there!!!

4. Mar 14, 2006

### nophun6

whoops, two things: i forgot to mention that in question 1 I nedd to find the magnetic force and direction on just the Lower section of the loop, and the second thing is i guess i wasnt thinking about the pi, thanks for pointing that mistake out.
If i am looking at just the lower section of the loop would it be: F= IBLSin(theta) where theta is 90??
thanks.

5. Mar 14, 2006

### nrqed

Ah.. ok. Yes, then theta is 90. I assume you know how to get the direction of the force...