1.

A bar magnet of l length and magnetic dipole moment M is bent in the form of an arc as shown in the figure. The new magnetic dipole moment will be

Answer»

M
`3/pi M`
`2/piM`
`M/2`

Solution :As we KNOW that, `M = m xx l therefore m = M/l` …..(i)
We assume that the POLES are situated at the ends.
`"Angle" = "arc"/"RADIUS"`
`therefore pi/3 = ("Arc"AB)/r="length of the magnet (l)"/r`
`r=l/(pi//3)=(3l)/pi` ….(ii)
But after bending the poles are at A and B.
Distance `AB = AO + OB = rsintheta + rsintheta`
`=2R sin theta= 2r xx 1/2=r`
`therefore` New magnetio moment, m. = mr
From (i) and (ii),
`M. = M/l xx(3l)/pi xx (3M)/pi`


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