Two concentric coils of 10 turns each are placed in the same plane. Their radii are 20 cm and 40 cm and carry 0.2 A and 0.3 A current respectively in opposite directions. The magnetic induction (in tesla) at the centre is

Options

A. `3/4mu_(0)`
B. `5/4mu_(0)`
C. `7/4mu_(0)`
D. `9/4mu_(0)`

Answer

B

Explanation

`B=(10xxmu_(0)xx0.2)/(2xx0.2)-(10xxmu_(0)xx0.3)/(2xx0.4)=5/4mu_(0)`