Q. A magnet of magnetic moment M and length 2l is bent at its mid-point such that the angle of bending is 60°. The new magnetic moment is.
(a) M
(b) M/2
(c) 2M
(d) M/√2
Ans: (b)
Solution : When a magnet is bent at its mid-point , each half having magnetic moment M/2 & angle between them is 120°
The new magnetic moment is
$\displaystyle M’ = \sqrt{(\frac{M}{2})^2 + (\frac{M}{2})^2 + 2 \times \frac{M}{2} \times \frac{M}{2} \times cos120}$
$ \displaystyle M’ = \sqrt{(\frac{M^2}{4}) + (\frac{M^2}{4}) + 2 \times \frac{M}{2} \times \frac{M}{2}\times \frac{-1}{2}}$
$ \displaystyle M’ = \frac{M}{2} $