# Two coaxial circular coils

1. Jun 28, 2012

### Curious314

1. The problem statement, all variables and given/known data
Two coaxial circular coils of radius R = 15 cm, each carrying 4.0 A in the same direction, are positioned a distance d = 20 cm apart, as shown in the figure. Calculate the magnitude of the magnetic field halfway between the coils along the line connecting their centers. (μ0 = 4π × 10-7 T ∙ m/A)

2. Relevant equations

3. The attempt at a solution

so:

B= [(4*∏*10-7)(4.0)(0.152)]/[2*(0.152+0.22))3/2]

which is = 3.62 x 10-6

not near any of the options.
Is this a very wrong approach?

Thanks!

2. Jun 28, 2012

### Infinitum

Hi!

You are only considering the field due to one of the coil at a distance 20cm from its center. But you are asked the total magnetic field due to both, halfway from their centers! So fields from each of the loop will add. Remember to check the field direction due to each before adding, as it is a vector.

3. Jun 28, 2012

### Curious314

Thank you!!!!!!!!!!