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` approximately
C. `8:1` approximately
D. `1:1` approximately

Answer

c

Explanation

(c) Taking distance from the centre of the magnet,
`(B_(1))/(B_(2))=((x_(2))/(x_(1)))^(3)=((2x+1)/(x+1))^(3)=8:1`, approximatly.