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When radiation of wavelength λ is incident on a metallic surface, the stopping potential of ejected photoelectrons is 4.8 V. If the same surface is illuminated by radiation of double the previous wavelength, then the stopping potential becomes 1.6 V. The threshold wavelength of the metal is

Asked in JEE Main 25th July 2nd Shift 2021 · Stopping potential from wavelength

Answer: (1) 4λ

Step-by-step solution

Given: V₀=4.8 V at λ and 1.6 V at 2λ.

Subtracting the two equations: (hc)/(2λ)=3.2e, so (hc)/λ=6.4e.

φ=6.4e-4.8e=1.6e.

λ₀=(hc)/φ=(6.4eλ)/(1.6e)=4λ.

Why the other options are wrong

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