CBSE Class 10 Answered

(a) A magnetic field line is the path along which a free north-pole tends to move. The direction of a magnetic field at a point is determined by placing a small compass needle. The N - pole of compass indicates the direction of magnetic field at that point.

(b)

(c) The properties of magnetic field lines are as follows.

1. Magnetic field lines emerge from the North pole and merge at the South pole.
2. The strength of the magnetic field is shown by the degree of closeness of the field lines. The field is stronger where the field lines are crowded. 
3. Magnetic lines do not intersect with each other.