Question

Two wires are wound into coils of one turn and three turns of equal radius. If the same current is passed through the coils, the ratio of magnetic field at their centres will be:

• A. 1:4
• B. 1:9
• C. 9:1
• D. 1:3

Answer 1

The correct option is B 1:9

$B\alpha n^2\frac{B_1}{B_2}={\left[\frac{n_1}{n_2}\right]}^2={\left[\frac{1}{3}\right]}^2{B}_1:B_2=1:9$