Explain the method of plotting magnetic field lines by using a small compass needle.

Explanation

(i) A white piece of paper is fixed on a board. The bar magnet is placed at the middle.
(ii) The magnetic needle is placed close to the north pole of the magnet
(iii) The south pole of the compass needle will point the north pole of the magnet.
(iv) A dot mark is put on the paper in the direction pointed by the north pole of the compass needle.
(v) The compass needle is now so placed that its south pole points the dot.
(vi) A dot mark is put on the paper in the new direction pointed by the north pole of the compass needle. (vii)Steps (v) and (vi) are repeated till the compass
reaches the south pole of the bar magnet.
(viii)All the dots are joined to obtain a magnetic field line of the bar magnet.