# Homework Help: Magnetic Field with three parallel wires

1. Dec 1, 2012

### rikinmathur

1. The problem statement, all variables and given/known data
Three long, straight wires are carrying currents that have
the same magnitude. In C the current is opposite to that
in A and B. The wires are equally spaced. Each wire experiences a net force due to the other two wires. Which
wire experiences a net force that has the greatest magnitude?

A =====>====
B=====>====
C=====<====

2. Relevant equations
FAB = μ°I1 I2 / 2∏d

3. The attempt at a solution
It says that the answer is B because 2I squared / d is the net force on B. But the way I am doing it is -I^2/d + I^2/d = 0, hence the net forces cancel out and the force on B is zero. I don't understand how it is 2I^2/d. Please help.

2. Dec 1, 2012

### Saitama

Hi rikinmathur! Welcome to pf!

What are the direction of forces on wire B due to the other two wires?

3. Dec 1, 2012

### Tarti

Hey rikinmathur, just think in terms of charges, maybe this is easier for you: A and B are positively charged (in a magnetic sense) and C is negative. So, which wire-pairs will experience an attractive and which a repulsive force?