On meter length of wires carriers a constant current. The wire is bent to from a circular loop. The magnetic field at the centre of this loop is `B`. The same is now bent to form a circular loop of smaller radius to have four turns in the loop. The magnetic field at the centre of this loop `B`. The same is now bent to form a circular loop of smaller radius of have four turns in the loop. The magnetic field at the centre of this new loop is

Options

A. `4B`
B. `16B`
C. `B//2`
D. `B//4`

Answer

B

Explanation

`B'=n^(2)B implies B'=(4)^(2)B=B'=16 B`