The couple acting on a magnet of length 10 cm placed in a uniform magnetic field of intensity `40 NA^(-1)m^(-1)` such that the axis of the magnet makes `45^(@)` with the field direction is `sqrt2/10 Nm`. The pole strength of the magnet (in Wb) is

Options

A. `5xx10^(-3)`
B. 0.5
C. 0.05
D. 5

Answer

C

Explanation

Couple acting on a magnet, `tau=MB"sin"theta`
`(sqrt2)/(10)=Mxx40xx"sin"45^(@)`
`implies M=(sqrt2xxsqrt2)/(40xx10)=1/200`
`implies M=mxx2l`
`implies M=(M)/(2l)=(1)/(200xx10xx10^(-2))`
`=(1)/(2xx10)=0.05`