Two identical bar magnets are fixed with their centres at a distance $d$ apart. A stationary charge $Q$ is placed at $P$ in between the gap of the two magnets at a distance $D$ from the centre $O$ as shown in the figure. The force on the charge $Q$ is:

If a diamagnetic substance is brought near the north or the south pole of a bar magnet, it is

The variation of susceptibility ($\chi$) with absolute temperature ($T$) for a paramagnetic material is represented as:

If $\theta_1$ and $\theta_2$ be the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip $\theta$ is given by:

A magnetic needle suspended parallel to a magnetic field requires $\sqrt{3}$ J of work to turn it through $60^\circ$. The torque needed to maintain the needle in this position will be:

An iron bar of length $L$ has a magnetic moment $M$. It is bent at the middle of its length such that the two arms make an angle $60^{\circ}$ with each other. The magnetic moment of this new magnet is:

Above Curie temperature:

The magnetic susceptibility is negative for:

The following figures show the arrangement of bar magnets in different configurations. Each magnet has a magnetic dipole moment $\mathbf{m}$. Which configuration has the highest net magnetic dipole moment?