Solving Magnetic Field & Current Direction Problems

[superslow991]

Homework Statement

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)

Homework Equations

B1 = μo I r2 / [ 2 (r2 + x2 ) 3/2 ]

i2 = i1*(B2/B1)

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?

 

[BvU]

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html
Assume both coils are aligned with the x axis

 

[gneill]

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".

 

[BvU]

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".

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 ?