Question

Assertion $\left(A\right)$ : Magnetic moment of an atom is due to both, the orbital motion and spin motion of every electron.

Reason $\left(R\right)$ : A charged particle at rest produces a magnetic field.

• A. Both $\left(A\right)$ and $\left(R\right)$ are true, $\left(R\right)$ is the correct explanation of $\left(A\right)$
• B. Both $\left(A\right)$ and $\left(R\right)$ are true, $\left(R\right)$ is not the correct explanation of $\left(A\right)$
• C. $\left(A\right)$ is true but $\left(R\right)$ is false.
• D. $\left(A\right)$ is false but $\left(R\right)$ is true.

Answer 1

The correct option is C $\left(A\right)$ is true but $\left(R\right)$ is false.

As we know, current loop has magnetic moment, here the moving electrons behaves as current loops. Thus, the magnetic moment associated with electron motion is,

$\mu =IA=q\left(\frac{v}{2\pi r}\right)\times \pi r^2=\frac{evr}{2}[\because q=e]$

$\because L=mvr\Rightarrow vr=\frac{L}{m}$

$\Rightarrow \mu =\frac{eL}{2m}$

It is also possible that, magnetic moment due to spin motion of electrons.

But a charged particle at rest will not produce the magnetic field. It will only produce electric field.

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(C\right)$ is the correct answer.