(a) Name the poles P, Q, R and S of the magnets in the following figures 'a' and 'b'.

(b) State the inference drawn about the direction of the magnetic field lines on the basis of these diagrams.

Hint

Use the equation F = BIL sin$\theta$ to find the force experienced by the conductor.

Quick oral answer

The force experienced by a current-carrying straight conductor placed in a uniform magnetic field is maximum when the direction of the current is perpendicular to the direction of the magnetic field. This is because the force experienced by the conductor is given by the equation F = BIL sin$\theta$, where F is the force, B is the magnetic field strength, I is the current, L is the length of the conductor, and $\theta$ is the angle between the direction of the current and the direction of the magnetic field. When the direction of the current is perpendicular to the direction of the magnetic field, $\theta$ = 90$^\circ$, and sin$\theta$ = 1. Therefore, the force experienced by the conductor is maximum when the direction of the current is perpendicular to the direction of the magnetic field.