Question

The effective length of a magnet is $31.4cm$ and its pole strength is $0.5A-m$. The magnetic moment, if it is bent in the form of a semicircle will be:

• A. $0.1A-m^2$
• B. $0.01A-m^2$
• C. $0.2A-m^2$
• D. $1.2A-m^2$

Answer 1

Answer: (A)

Circumference of a circle of radius $r$ is $2\pi r$ .
Magnetic moment $(M)$ is a measure of the strength of a magnetic source.
It is denned as pole strength $(m)$ multiplied by distance $(d)$
$M=md$ Circumference of semicircle is $\pi \frac{d}{2}$ .
Given, $d=31.4cm=31.4\times {10}^{-2}m$
$l=\frac{\pi d}{2}$
$0.314=\frac{3.14}{2}\times d$
$\Rightarrow$ $d=0.2m$ .
So, magnetic moment $=0.5\times 0.2$
$=0.1A-m^2$ ,