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Question: Answered & Verified by Expert
A charged particle (charge $q$ ) is moving in a circle of radius $R$ with uniform speed $v$. The associated magnetic moment $\mu$ is given by
PhysicsMagnetic Effects of CurrentJIPMERJIPMER 2009
Options:
  • A $\frac{q v R}{2}$
  • B $q v R^2$
  • C $\frac{q \nu R^2}{2}$
  • D $q v R$
Solution:
2957 Upvotes Verified Answer
The correct answer is: $\frac{q v R}{2}$
As revolving charge is equivalent to a current, so
$\begin{aligned}
& I=q f=q \times \frac{\omega}{2 \pi} \\
But \quad & \omega=\frac{v}{R}
\end{aligned}$
where $R$ is radius of circle and $v$ is uniform speed of charged particle.
Therefore,
$I=\frac{q v}{2 \pi R}$
Now, magnetic moment associated with charged particle is given by
or
$\begin{aligned}
\mu & =I A=I \times \pi R^2 \\
or \quad \mu & =\frac{q v}{2 \pi R} \times \pi R^2 \\
& =\frac{1}{2} q v R
\end{aligned}$

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