Question

Two coplanar concentric circular coils have radii and Both have the same number of turns ''n''. The smaller coil carries a clock wise current ''i'', while the larger coil carries an anticlockwise current ''2i''. The magnetic field induction at the centre is

• A. $3\mu_0$ in / 4r
• B. zero
• C. $\mu_0$ in / 4r
• D. $\mu_0$ in / 2r

Answer 1

Answer: (B)

zero

Answer 2

$B=\frac{\mu_0n \,i}{2\pi};B_R=B_1-B_2$