When light of frequency twice the threshold frequency is incident on the metal plate, the maximum velocity of emitted election is \(v _{1}\). When the frequency of incident radiation is increased to five times the threshold value, the maximum velocity of emitted electron becomes \(v _{2}\). If \(v _{2}= x\) \(v _{1}\), the value of \(x\) will be...........

A \(8\)
B \(7\)
C \(2\)
D \(55\)

Verified Solution

Answer & Solution

Correct Answer

(C) \(2\)

Step-by-step Solution

Detailed explanation

\(hv =h v _{\text {th }}+\frac{1}{2} mv ^{2}\) \(v =2 v _{\text {th }}\) \(2 hv _{\text {th }}=h v _{\text {th }}+\frac{1}{2} mv _{1}^{2} \ldots \ldots(1)\) \(v =5 v _{\text {th }}\) \(5 hv _{\text {th }}=h v _{\text {th }}+\frac{1}{2} mv _{2}^{2} \ldots(2)\)…

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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