Question

Question 5.14: If the bar magnet in exercise 5.13 is turned around by 180º, where will the new null points be located?

Class 12 - Physics - Magnetism And Matter Magnetism And Matter Page-201

Answer 1

when the bar magnet is turned through 180°, neutral points would lie on equatorial line, so that magnetic field at equatorial line = horizontal component of earth's magnetic field
e.g., $B_2=\frac{\mu_0}{4\pi}\frac{M}{d_2^3}=B_H$----(1)

in previous question, exercise 5.13
magnetic field at axial line =horizontal component of earth's magnetic field.
e.g.,$B_1=\frac{\mu_0}{4\pi}\frac{2M}{d_1^3}=B_H$----(2)

from equations (1), and (2),
$\frac{\mu_0}{4\pi}\frac{M}{d_2^3}=\frac{\mu_0}{4\pi}\frac{2M}{d_1^3}\\\\\therefore\:d_2^3=\frac{d_1^3}{2}$

given, $d_1$=14cm
so,$d_2^3=\frac{14^3}{2}$
$d_2=11.1cm$