Point `A` and `B` are situated along the extended axis of `2 cm` long bar magnet at a distance x and `2x cm` respectively. From the pole nearer to the points, the ratio of the magnetic field at `A` and `B` will be

Options

A. 4:1 exactly
B. 4:1 approx.
C. 8:1 exactly
D. 8:1 approx.

Answer

D

Explanation

For a magnet `B=mu_(0)/(4pi).(2M)/x^(3)` (Nearly)
`rArr B_(1)/B_(2)=(x_(1)/x_(2))^(3)=(x/(2x))^(3)=1/8` (Approx.)