A bar magnet of length ‘l’ and magnetic dipole moment

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

1. 3 M
  π
2. 2 M
  π
3. M
  2
4. M

Correct Option: A

Magnetic dipole moment
M = m × l
M' = m × r
From figure

l =	πr	or r =	3l
	3		π

so. M' = m × r =	m × 3l	=	3	M
	π		π