# Homework Help: Magnetic force

1. Jan 16, 2010

### sArGe99

I know that two infinitely long straight conductors will attract each other when kept parallel if current flows in the same direction in both.
If two circular loops are placed such that their planes are parallel, current in the same direction, will they attract?

Also, does a loop carrying current experience any force if placed in a uniform magnetic field.
F = I (l X B)
l is a vector, so I believe l=0 for a loop since the initial and terminal points are the same. Is that correct?

2. Jan 16, 2010

### yuqiao

for ur last question, i have to say that it is incorrect to say l=0. if u know some calculus, u will have to deal with an infinitely small arc and then add them up. another way to think about it is to consider the loop a magnetic bar placed in a magnetic field. apparently, f is not 0

3. Jan 16, 2010

### sArGe99

Oh.. Circular loop as an equivalent bar magnet.
I thought vector l = vector l(final) - vector l(initial)
Final and initial points are the same for a circular loop, so l=0