Question

How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.

Answer 1

Behavior of Solenoid

1. A coil of wire wound uniformly over a hollow nonconducting cylinder having a length large compared with its radius, is said to constitute a solenoid.
2. When a current is passed through the coil a uniform magnetic field is produced inside the coil parallel to its axis.
3. Therefore, the solenoid starts behaving as a magnet.
4. If ${\mu }_0$ is the permeability of free space, $n$ is the number of turns per unit length and $I$ is the current passing through the coil, then the uniform magnetic field $\overrightarrow{B}$in the $x$ direction is, $\overrightarrow{B}=\hat{x}{\mu }_{0}nI$

Poles of Solenoid

The poles of the current-carrying solenoid can be determined in the following way:

1. Using a brass hook the solenoid is made to hang freely.
2. A bar magnet is placed near the solenoid in such a way that the north pole of the magnet is kept closer to the solenoid.
3. We know that like poles repel and unlike poles attract.
4. Hence, if the solenoid moves away from the magnet, it means that the side of the solenoid facing the north pole of the bar magnet is the north pole, and the opposite side of the solenoid is the south pole.
5. On the other hand, if the solenoid moves towards the magnet, it means that the side of the solenoid facing the north pole of the bar magnet is the south pole, and the opposite side of the solenoid is the north pole.