A bar magnet of dipole moment M is bent at midpoint by 90° (in the form of the English alphabet ‘L’). The new magnetic dipole moment of the magnet will be:
A) M
B) M/√2
C) √2 M
D) M/2

When a bar magnet is bent at its midpoint by 90 degrees to form the English alphabet 'L', the magnetic dipole moment of the resulting configuration can be calculated as follows:

Let's assume that the original bar magnet has a magnetic dipole moment 'M' and the length of each arm of the 'L' shape is 'L'. When the magnet is bent at 90 degrees, the new magnetic dipole moment 'M_new' can be calculated as:

M_new = M × (length of one arm of the 'L').

The length of one arm of the 'L' is L/√2, because it forms a right-angled triangle with the original length 'L' as the hypotenuse and the shorter side being L/√2.

So,

M_new = M × (L/√2).

Now, we can simplify this expression:

M_new = M/√2.

So, the new magnetic dipole moment 'M_new' of the bent magnet is equal to 'M/√2'.

Therefore, the correct option is:

B. M/√2