CBSE Class 10 Science 2022 · Paper 31/1/2 · Question 14

(a) The diagram shows the bar magnet at the centre, with its N and S ends, and the iron filings lying end to end along curves that leave one end of the magnet, loop round and reach the other end. The curves are crowded near the two ends (the poles) and spread out farther away, and none of them crosses another (see the figure). (b) It demonstrates the magnetic field around the magnet: the magnet exerts a force on the filings in the region around it, and the lines along which the filings align themselves represent the magnetic field lines. The filings crowd near the poles, where the field is strongest. (c)(i) The direction of the magnetic field at a point is given by the tangent to the field line at that point, in the sense of the arrow on the line - the direction in which the north pole of a compass needle placed there points. Two field lines never cross, because at a crossing there would be two tangents, that is, two directions of the field at one point, and a compass needle placed there would have to point in two directions at once, which is not possible. OR (c)(ii) Fix a sheet of white paper on a drawing board, place the magnet on it and mark its boundary. Place a small compass near the north pole and mark both ends of the needle. Move the compass so that the south end of the needle sits where its north end was, and mark the north end again. Continue step by step until the compass reaches the south pole, and join the marks by a smooth curve: that is one field line. The drawing shows one such line above the magnet and one below it, each leaving the N pole and entering the S pole, with arrows from N towards S (see the figure).