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Question about two circular concentric coils

by phys62
Tags: circular, coils, concentric
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Feb17-09, 11:46 AM
P: 53
1. The problem statement, all variables and given/known data
Two circular coils are concentric and lie in the same plane. The inner coil contains 110 turns of wire, has a radius of 0.010 m, and carries a current of 5.6 A. The outer coil contains 190 turns and has a radius of 0.014 m. What must be the magnitude of the current in the outer coil, such that the net magnetic field at the common center of the two coils is zero?

2. Relevant equations

3. The attempt at a solution
Ok so I have I1=5.6 A
R1=.010 m
R2=.014 m

I think that I have to use that equation somehow and set them equal to each other, but I'm lost after that. Perhaps I'm using the wrong equation entirely? Any help is much appreciated!!

Edit: Do I just solve for B1 and then set that equal to the equation for the 2nd coil (only make it negative)?
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
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Feb17-09, 12:26 PM
HW Helper
P: 5,341
You should be able to figure the magnitude of the field from the first coil from what you're given.

Then they want to know what opposing current using the parameters of the other coil is needed to null out the B field at the center.

I find it easiest to keep it as variables of the 2 loops and then plug in the numbers at the end to solve for the one that you need.

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