Question

Why can \[B_2\] be assumed uniform across the entire area of the inner coil?

Options

• The two coil axes are perpendicular.

• The inner coil has a larger radius than the outer coil.

• The inner coil is very small compared to the outer coil: \[r_1\ll r_2\] .

• The outer coil carries no current.

Answer 1

When \[r_1\ll r_2\] , the inner coil occupies a small region near the outer coil’s centre. The field \[B_2\] can therefore be treated as uniform across its area.