Question

(a) What are magnetic lines of force?

(b) Do the lines of force really exist?

(c) Mention important properties of magnetic lines of force.

Answer 1

(a) Magnetic Lines of Force

(i) Imagine a small north magnetic pole is placed in the magnetic field created by a magnet, it will experience a force. The north pole will move under the influence of magnetic field. The path traced by a north pole free to move under the influence of magnetic field is called a magnetic line of force.

(ii) A line of force is a continuous curve in the magnetic field such that the tangent at any point of it gives the direction of the resultant field at that point.

The concept of magnetic lines of force is also used to represent the magnetic field in a region graphically.

(b) Actually the lines of force do not exist but are hypothetically considered to explain many phenomena in terms of lines of force.

(c) Properties of lines of force

1. They are closed and continuous curves.
2. They always start from the N-pole and terminate at the S-pole of the magnet.
3. The tangent at any point on a line of force gives the direction of magnetic field at the point. 
4. They never intersect one another because if two lines of force intersect, there would be two directions of magnetic field at that point which is impossible.
5. They are crowded near the poles where the magnetic field is strong and get separated where the magnetic field becomes weak.
6. Parallel and equidistant lines of force represent uniform magnetic field (such as the earth’s magentic field in a small region).
7. They behave like stretched elastic rubber strings.