CBSE Class 10 Science 2022 · Paper 31/1/3 · Question 14

(a) The iron filings line up along curves that start at one pole of the magnet, bend round its sides and end at the other pole, on both sides of the magnet; they are crowded near the two poles and more widely spaced farther away (see the figure). (b) The magnetic field of the bar magnet. In this field the iron filings experience a force that differs from point to point in magnitude and direction; each filing is magnetised and turns, like a tiny compass needle, to lie along the field where it is, so the filings arrange themselves along the magnetic field lines. Tapping only frees them to turn. (c)(i) The direction of the magnetic field at a point is the direction of the tangent to the field line at that point, in the sense of the arrow on the line; it is the direction in which the north pole of a compass needle placed there points. Two field lines never cross because at the point of crossing there would be two tangents, that is, two directions of the field at one point, and a compass needle there would have to point in two directions at once, which is not possible. OR (c)(ii) Place the magnet on a sheet of white paper fixed on a drawing board and mark its outline. Put a small compass near the N pole, mark the positions of both ends of its needle, then move the compass so that its south end lies on the mark of its north end and mark the new north end. Repeat step by step until the S pole is reached, and join the marks with a smooth curve: that is a field line, with its arrow in the direction in which the needle's north end pointed. One such line on each side of the magnet runs from the N pole round to the S pole, with the arrows from N to S outside the magnet (see the figure).