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 cms
B. `20 (2)^(1//3)` cms
C. `20(2)^(2//3)` cms
D. `20(2)^(3//3)` cms

Answer

b

Explanation

(b) Here, `d_(1)=20cm, M_(2) M_(1) , d_(2)=?`
`(M_(2))/(M_(1))=(d_(2)^(3))/(d_(1)^(3))=2rArrd_(2)=2^(1//3)d_(1)=20(2)^(1//3)cm`