A conducting solid sphere having uniform charge Q on it has radius R. It is rotating with anangular velocity ω. If a uniform magnetic field B is present perpendicular to axis of rotation then the torque on sphere will be

Options

A. `( q omega R ^(2))/(5) B`
B. `(q omega R ^(2))/(3) R`
C. `(q omega R ^(2))/(4)B`
D. `(q omega R ^(2))/(2) R`

Answer

B

Explanation

Magnetic moment of sphere is M then
`(M)/((2)/(3)m R ^(2) omega)= (q)/(2m)`
`implies M = (q omega R ^(2))/(3)`
Torque `= MB sin 90^(@) = (q omega R ^(2) B)/(2)`