Question

Two points A and B are located at distances 20cm
and 30 cm from the centre of a short bar magnet on
its axial line. The ratio of magnetic induction at A
and B is

I) 12:3

2) 3:2

3) 9:4

4) 27:8
​

Answer 1

Answer:

4)

Explanation:

pls follow me, see your answer

Answer 2

Answer:

The ratio of magnetic induction at A and B is 27:8.

Explanation:

Magnetic field at axial point B=

                                $B=\frac{\mu_0}{4 \pi}\times \frac{2 M}{x^{3}}$,

B=The magnetic field.

μ₀=Absolute permeability of free space.

m=Magnetic strength of each pole.

x = Distance of the pole from the point.

$B_A= Magnetic strength at point A here x=30cm\\\\B_B= Magnetic strength at point B here x=20cm$

${B}_A=\frac{\mu_{0}}{4 R} \times \frac{2 \pi}{(20)^{3}} \\ B_{B}=\frac{\mu_{0}}{4 \pi} \times \frac{2 M}{(30)^{3}} \\ \frac{B_{A}}{B_{B}}=\frac{(30)^{3}}{20)^{3}}=\frac{27}{8} =27: 8$