COMEDK · Physics · 27. Dual Nature of Matter

Threshold wavelength for photoelectric emission from a metal surface is \(5200\) \(Å\). Photoelectrons will be emitted, when this surface is illuminated with monochromatic radiation from

A \(1 \mathrm{~W~IR}\) lamp
B \(50 \mathrm{~W~UV}\) lamp
C \(50 \mathrm{~W~IR}\) lamp
D \(10 \mathrm{~W~IR}\) lamp

Verified Solution

Answer & Solution

Correct Answer

(B) \(50 \mathrm{~W~UV}\) lamp

Step-by-step Solution

Detailed explanation

Given, \(\lambda_{0}=5200 Å=5200 \times 10^{-10} \mathrm{~m}\) \(\therefore\) Threshold frequency, \(f_{0}=\frac{c}{\lambda_{0}}=\frac{3 \times 10^{8}}{5200 \times 10^{-10}}\) \(=5.76 \times 10^{14} \mathrm{~Hz}\) It lies in the frequency range of UV-rays, so…

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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