# Homework Help: Magnetic Force in a current carrying coil

1. Mar 28, 2010

### nhartung

1. The problem statement, all variables and given/known data
A rectangular loop with length of l = 0.30 m and width w = 0.12 m and a mass of 25-grams falls (from rest) a distance of .28 m before entering a constant magnetic field that points out of the page. The internal resistance of the wire is 5.5 $$\Omega$$.

(i) What is the speed of the loop when it first enters BOut. (The magnetic field).

Here I think i can just use v = $$\sqrt{2gd}$$ = 2.34 m/s. (correct me if this is an incorrect way of finding this.)

(ii) If, while the loops enters the magnetic field, it moves at a constant speed, then what is the magnetic force.

Here I'm stuck but im thinking there is just some equation that I am missing but i've been searching my book and haven't found anything helpful.

(iii) What is the magnitude of the magnetic field BOut.

(iv) What is the magnitude of the induced current.

I'm thinking I can use I = $$\frac{LBsinø}{F}$$ for this..

I just want to focus on (ii) right now because I think (iii) and (iv) depend on (ii)'s answer and hopefully are easy.

Last edited: Mar 28, 2010
2. Mar 29, 2010

### nhartung

Ok I think i've worked out (ii) Since the loop has constant velocity this means the acceleration is zero. This must mean the Force of Gravity and Magnetic Force are canceling each other (they are equal) which means F = mg = 245.25N. I still need some help on (iii) and (iv) though.