Assertion (A) : Magnetic field lines never intersect each other.

Reason (R) : At a particular point, magnetic field has only one direction.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : Neutral points are the points at which two magnetic fields are equal in magnitude and in the same direction.

Reason (R) : The net magnetic field at a neutral point is zero.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

In a physics laboratory, a student places a bar magnet near a compass. At certain positions, the compass needle shows no deflection.

(a) Why does the compass needle show no deflection at certain points? What are these points called?

(b) What happens to the magnetic field lines at these points?

(c) Why are these points useful in studying magnetic fields?

(d) Are these points fixed, or do they change their positions?

Ravi observed that an electromagnet could lift iron pieces only when electric current was flowing through it. When the current was switched off, the iron pieces fell down.

(a) Why does an electromagnet lose its magnetism when the current stops?

(b) How is an electromagnet different from a permanent magnet?

(c) How can the strength of an electromagnet be increased?

(d) Why are electromagnets preferred in cranes?

(e) Which material is preferred for making the core of an electromagnet?