Two circular coil of radii 5cm and 10cm carry equal currents of 2A. The coils have 50 and 100 turns, respectively, and are placed in such a way that their planes as well as their centers coincide. Magnitude of magnetic field at the common centre of coils is

Options

A. `8pi xx 10^(-4)T` if current in the coils are in same sense.
B. `4pi xx 10^(-4)T` if current in the coils are in opposite sense
C. zero if current in the coils are in opposite sense
D. `8pi xx 10^(-4)T` if current in the coils are in opposite.

Answer

A, C

Explanation

Using magnetic field at the centre of a circular coils is, `B= (mu_(0)NI)/(2R)`
We get, `|vec(B)_(1)| = |vec(B)_(2)| =4pi xx 10^(-4)T`
If current in same sense `B_("net")= 8pi xx 10^(-4)T`
If current in opposite sense `B_("net")=0`