# Homework Help: Biot Savart law

1. Apr 2, 2017

### superslow991

1. The problem statement, all variables and given/known data

Two circular coils of diameter 30.0 cm are parallel to each other and have their centers along the same line L but separated by 22.0 cm. When an experimenter views the coils along L, the coil closer to her carries a clockwise current of 2.50 A. Find the magnitude and sense (clockwise or counterclockwise) of the current needed in the other coil so that the net magnetic field on L midway between the two coils will have a magnitude of 4.10 µT and point away from the experimenter who is viewing the coils along L. (μ0 = 4π × 10-7 T ∙ m/A)

2. Relevant equations
B1 = μo I r2 / [ 2 (r2 + x2 ) 3/2 ]

i2 = i1*(B2/B1)

3. The attempt at a solution
Trying to figure out the direction of the coils, field, and current. I believe the magnetic field is in direction of the current? the current is in direction of the length?

2. Apr 2, 2017

3. Apr 2, 2017

### Staff: Mentor

The problem doesn't state how many turns there are in the coils. Perhaps they are single loops?

It might be beneficial to investigate: "Helmholtz coils".

4. Apr 3, 2017

### BvU

I thought of that, but wasn't sure -- the OP doesn't mention any length, even though that is rather important information. Is it so that 'coil' includes 'zero-length' coils and 'solenoid' usually refers to longer cylinders, or are both terms completely equivalent ?