Question

The diagram shows a rectangular coil ABCD, suspended freely between the concave pole pieces of a permanent horseshoe magnet, such that the plane of the coil is parallel to the magnetic field.

1. State your observation when the current is switched on.
2. Give an explanation for your observation in (i).
3. State the rule, which will help you to find the motion of rotation of the coil.
4. In which position will the coil ultimately come to rest?
5. State four ways of increasing the magnitude of force acting on the coil.

Answer 1

1. The coil ABCD will turn. The arm AB of the coil will move out of the plane of the paper and arm CD into the plane of the paper. Thus, the coil will turn in the anticlockwise direction.
2. A magnetic field is set up by the coil due to the passage of electric current. The magnetic field of the coil is at right angles to the magnetic field of the permanent magnet. Thus, a magnetic couple acts, which turns the coil.
3. Fleming’s left rule: It states: Stretch the thumb, the forefinger, and the middle finger of the left hand such that the forefinger points in the direction of the magnetic field and the middle finger points in the direction of the current. Then, the thumb points in the direction of motion of the conductor.
4. The coil will come to rest at right angles to the direction of the magnetic field.
5. 1. By increasing the number of turns in the coil.
   2. By increasing the area of the cross-section of the coil.
   3. By placing a laminated soft iron core within the coil.
   4. By increasing the magnitude of the current coil.