A student sketches magnetic field lines around a bar magnet

PHYSICS · Single correct · CBSE · Physics · Magnetism and Matter · Magnetism and Matter

Problem

A student sketches magnetic field lines around a bar magnet. She finds that 15 lines cross a straight segment of length

3\,\text{cm}

drawn near the north pole, while only 5 lines cross an equal segment drawn

6\,\text{cm}

away from that pole along its axis. Which relation correctly compares the magnetic field strengths

B_1

(near the pole) and

B_2

(farther away)? (a)

B_1 = B_2

(b)

B_1 = 3 B_2

(c)

B_1 = \dfrac{5}{3} B_2

(d)

B_1 = \dfrac{1}{3} B_2