Q. The effective length of a magnet is $31.4 \,cm$ and its pole strength is $0.5 \,A-m$. The magnetic moment, if it is bent in the form of a semicircle will be:
Delhi UMET/DPMTDelhi UMET/DPMT 2003
Solution:
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=31.4\,cm=31.4\times {{10}^{-2}}m $
$ l=\frac{\pi d}{2} $
$ 0.314=\frac{3.14}{2}\times d $
$ \Rightarrow $ $ d=0.2\,m $ .
So, magnetic moment $ =0.5\times 0.2$
$=0.1\,\,A-{{m}^{2}} $ ,
