Two short magnets have equal to pole strength but one is twice as long as the other. The shorter magnet is placed 20 cm in tan A position from the compass needle. The longer magnet must be placed on the other side of the magnetometer for no deflection at a distance equal to:

Options

A. `20 cm`
B. `20xx(2)^(1//3) cm`
C. `20xx(2)^(4//3) cm`
D. `20xx(2)^(2//3) cm`

Answer

B

Explanation

`mu/(4pi)((2M_(1))/r_(1)^(3))=mu_(0)/(4pi)((2M_(2))/r_(2)^(3))`
`:. M_(1)/M_(2)=(r_(1)/r_(2))^(3) `
or `(1)/(2) = ((20)/(r_(2))^(3) rArr r_(2) = 20(2)^(1/3) cm`