Question

The pole strength of 12 cm long bar magnet is 20 A m. The magnetic induction at a point 10 cm away from the centre of the magnet on its axial line is `[(mu_(0))/(4pi)=10^(-7)"H m"^(-1)]`
A. `1.17xx10^(-3)` T
B. `2.20xx10^(-3)` T
C. `1.17xx10^(-2)` T
D. `2.20xx10^(-2)` T

Answer 1

Correct Answer - A
On axial line, `B=(mu_(0))/(4pi)(2md)/((d^(2)-l^(2))^(2))`
Given, `2l=` 12 cm, = 0.12 m
Pole strength = 20 A m, `d` = 10 cm = 0.1 m
Magnetic moment `m= 20xx0.12` A `m(2)`
`therefore" "B=10^(-7)xx(2(20)xx(0.12)xx0.1)/([(0.1)^(2)-(0.06)^(2)]^(2))=1.17xx10^(-3)` T