Question

Question 5.13: A short bar magnet placed in a horizontal plane has its axis aligned along the magnetic north-south direction. Null points are found on the axis of the magnet at 14 cm from the centre of the magnet. The earth’s magnetic field at the place is 0.36 G and the angle of dip is zero. What is the total magnetic field on the normal bisector of the magnet at the same distance as the null−point (i.e., 14 cm) from the centre of the magnet? (At null points, field due to a magnet is equal and opposite to the horizontal component of earth’s magnetic field.)

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

Answer 1

A/C to question,
angle of dip is zero at the palace , so the earth's magnetic field is uniform with magnitude 0.36G in the direction geographical south to geographical north as shown in figure.

At axial position for full point.
$B_H=B_A=0.36G$
and at equatorial position the field due to bar magnet is $\frac{B_A}{2}$ as we know,
so, $B_E=\frac{B_A}{2}=0.18G$

now, total magnetic field of earth and magnet adds at equatorial position.
$B_{total}=B_H+B_E$
= 0.36G + 0.18G = 0.54G