Question

The pole strength of a 12 cm long bar magnet is 20 A.m. The magnetic induction at a point 10 cm along from the centre of the magnet on its axial line is

• A. 1.1 x 10${}^{-3}$ T
• B. 2.2 x 10${}^{-2}$ T
• C. 3.3 x 10${}^{-2}$ T
• D. 11 x 10${}^{-2}$ T

Answer 1

Answer: (A)

1.1 x 10${}^{-3}$ T

$l=12cm$
$d=10cm$
$P=20Am$
$B_1=\frac{{\mu }_{0}P}{4\pi {(d-a)}^2}$
$B_2=\frac{{\mu }_{0}P}{4\pi (d+a)}$
$B=$ $B=B_1-B_2$
$=\frac{{\mu }_{0}P}{4\pi }(\frac{1}{{(d-a)}^2}-\frac{1}{{(d+a)}^2})$
$={10}^{-7}\times 20\times \frac{2\times 2\times 6\times 10}{{({10}^2-6^2)}^2}$
$=1.1\times {10}^{-3}T$