Question

Following figure show the arrangement of bar magnets in different configurations. Each magnet has magnetic dipole moment $M$. Which configuration has highest net magnetic dipole moment?

• A. (i)
• B. (ii)
• C. (iii)
• D. (iv)

Answer 1

The correct option is A (i)

Torque produced in a bar magnet is given by

$\tau =M\times B$

$\tau =MB\sin \theta$

where $\theta$ is the angle between $M$ and $B$

Torque for first orientation is:

${\tau }_1=MB\sin 90=MB$

Torque for second orientation is:

${\tau }_2=MB\sin 0=0$

Torque for first orientation is:

${\tau }_3=MB\sin 30=\frac{MB}{2}$

Torque for first orientation is:

${\tau }_4=MB\sin 60=\frac{\sqrt{3}MB}{2}$

Torque is maximum in case 1 and hence maximum net dipole moment.