Question

The diagram below shows an insulated copper wire wound around a hollow cardboard cylindrical tube. Answer the questions that follow:

1. What are the magnetic poles at A and B when the key K is closed?
2. State two ways to increase the strength of the magnetic field in this coil without changing the coil.
3. If we place a soft iron bar at the centre of the hollow cardboard and replace the DC source with an AC source then will it attract small iron pins toward itself when the current is flowing through the coil?

Answer 1

1. As the anticlockwise flow of current will occur at A, north pole will be produced at A; and as · clockwise flow of current will occur at B, the south pole will be produced at B.
2. In order to increase the strength of the magnetic field in this coil, one can increase the number of turns on the coil and/or increase the current flow and/or place an iron core inside the hollow cardboard cylindrical tube.
3. If we place a soft iron bar at the centre of the hollow cardboard and replace the DC source with an AC source then there will be no attraction of small iron pins toward itself when the current is flowing through the coil. This is because AC will not create any magnetic effect, though it is a flow of free charged particles.