Two concentric circular coils of ten turns each are situated in the same plane. Their radii are 20 and 40 cm and they carry respectively 0.2 and 0.4 ampere current in opposite direction, The magnetic field in weber / `m^2` at tteh centre is

Options

A. `(35)/(4) mu_(0)`
B. `(mu_(0))/(80)`
C. `(7)/(80) ""mu_(0)`
D. `(5)/(4) ""mu_(0)`

Answer

D

Explanation

`B_("net") = (mu_(0) N)/(2) [ (I_(1))/(r_(1)) - (I_(2))/(r_(2))]`
`= (10 mu_(0))/(2) [ (0.2)/(0.2) - (0.3)/(0.4)] = (5)/(4) mu_(0)`