An electron moves with a constant speed $v$ along a circle of radius $r$. Its magnetic moment will be ($e$ is the electron's charge)]
A$evr$
B$\frac{1}{2}evr$
C$\pi {r^2}ev$
D$2\pi rev$
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B$\frac{1}{2}evr$
b (b) $M = i\;(\pi {r^2}) = \frac{{ev}}{{2\pi r}} \times \pi {r^2} \Rightarrow M = \frac{1}{2}evr$
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