Two circular coils of radii 5.0 cm and 10 cm carry equal currents of 2.0 A. The coils have 50 and 100 turns respectively and are placed in such a way that their planes as well as the centres coincide. Find the magnitude of the magnetic field B at the common centre of the coils if the currents in the coils are (a) in the same sense (b) in the opposite sense.

Options

A. `8pixx10^-4T` if current in the coils are in same sense
B. `4pixx10^-4T` if current in the coils are in opposite sense
C. zero if current in the coils are in opposite sense
D. `8pixx10^-4T` if current in the coils are in opposite sense

Answer

A, C

Explanation

(a,c):
Using `B=(mu_0NI)/(2R)`
`|vecB_1|=|vecB_2|=4pixx10^-4T`
If current in same sense `B_(n et)=8pixx10^-4T`
If current in opposite sense `B_(n et)=0`