MHT CET · Physics · Electromagnetic Induction

An electron (mass \(\mathrm{m}\) ) is accelerated through a potential difference of ' \(\mathrm{V}\) ' and then it enters in a magnetic field of induction ' \(\mathrm{B}\) ' normal to the lines. The radius of the circular path is (e = electronic charge \()\)

A \(\sqrt{\frac{2 \mathrm{eV}}{\mathrm{m}}}\)
B \(\sqrt{\frac{2 \mathrm{Vm}}{\mathrm{eB}^2}}\)
C \(\sqrt{\frac{2 \mathrm{Vm}}{\mathrm{eB}}}\)
D \(\sqrt{\frac{2 \mathrm{Vm}}{\mathrm{e}^2B}}\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(\sqrt{\frac{2 \mathrm{Vm}}{\mathrm{eB}^2}}\)

Step-by-step Solution

Detailed explanation

Radius of circular path in a cyclotron is given by
\(\mathrm{R}=\frac{\mathrm{mV}}{\mathrm{qB}}\)
Here \(\mathrm{q}=\mathrm{e}\),
\(\therefore \quad \mathrm{R}=\frac{\mathrm{mV}}{\mathrm{eB}}... (i)\)
On entering the field,
\(\begin{aligned}
& \mathrm{KE}=\mathrm{eV}=\frac{1}{2} \mathrm{mv}^2 \\
\therefore \quad \mathrm{V} & =\sqrt{\frac{2 \mathrm{eV}}{\mathrm{m}}}... (ii)
\end{aligned}\)
Putting (ii) into (i),
\(\mathrm{R}=\frac{\mathrm{m} \sqrt{\frac{2 \mathrm{eV}}{\mathrm{m}}}}{\mathrm{eB}}=\sqrt{\frac{2 \mathrm{Vm}}{\mathrm{eB}^2}}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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