A very small magnet is placed in the magnetic meridian with its south pole pointing geographic north. The null point is obtained 20 cm away from the centre of the magnet. If the earth's magnetic field (horizontal component) at this point be 0.3 gauss, the magnetic moment of the magnet is

Question

A very small magnet is placed in the magnetic meridian with its south pole pointing geographic north. The null point is obtained 20 cm away from the centre of the magnet. If the earth's magnetic field (horizontal component) at this point be 0.3 gauss, the magnetic moment of the magnet is (A) 8.0 × 102 e.m.u. (B) 1.2 × 103 e.m.u. (C) 2.4 × 103 e.m.u. (D) 3.6 × 103 e.m.u.

Tardigrade Admin · Accepted Answer

At neutral points, |B|=|BH| ⇒ (2 M/(20)3)=0.3 ⇒ M=1.2 × 103 e.m.u. <img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/452c9c72221792afa1833206e9390921-.png" />

Q. A very small magnet is placed in the magnetic meridian with its south pole pointing geographic north. The null point is obtained $20 c m$ away from the centre of the magnet. If the earth's magnetic field (horizontal component) at this point be $0.3$ gauss, the magnetic moment of the magnet is

$8.0 \times 1 0^{2}$ e.m.u.

$1.2 \times 1 0^{3}$ e.m.u.

$2.4 \times 1 0^{3}$ e.m.u.

$3.6 \times 1 0^{3}$ e.m.u.

At neutral points,
$∣ B ∣ = ∣ B_{H} ∣ \Rightarrow \frac{2 M}{( 20 ) ^{3}} = 0.3$
$\Rightarrow M = 1.2 \times 1 0^{3}$ e.m.u.

Q. A very small magnet is placed in the magnetic meridian with its south pole pointing geographic north. The null point is obtained 20cm away from the centre of the magnet. If the earth's magnetic field (horizontal component) at this point be 0.3 gauss, the magnetic moment of the magnet is

8.0×102 e.m.u.

1.2×103 e.m.u.

2.4×103 e.m.u.

3.6×103 e.m.u.