Question

Select the correct answer about magnets with Magnetic Moment $M$ :
a) When $n$ identical magnets are arranged in the form of closed polygon with unlike poles nearer, the resultant magnetic moment is zero.
b) If one magnet is removed from the arrangement, resultant magnetic moment becomes $M$.
c) If one magnet is reversed in the polygon, the resultant magnetic moment of combination becomes $2M$

• A. a, b and c are correct
• B. a and b are correct but c is wrong
• C. only a is correct
• D. a, b and c are wrong

Answer 1

The correct option is A a, b and c are correct

Magnetic Moment is a vector quantity, so it follows vector addition.
Therefore effective length would be:
$1)0$, as all vectors will cancel each other
$2)L$ (but would be oriented in the opposite direction of the magnet if it was placed)

This can be proved from the first part, that if one magnet is removed the resultant of the two others will be M but in opposite direction to that which is removed.
$3)2L$

Again this can be proved from the first part, that the resultant of the (n-1) magnets will be M. Hence the two magnetic moments will add up, hence 2M.