Two monochromatic radiations of frequencies ν and ν/2 give stopping potentials Vₛ/2 and Vₛ, respectively. What is the threshold frequency?
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Question

Two monochromatic radiations of frequencies ν and ν/2 give stopping potentials Vₛ/2 and Vₛ, respectively. What is the threshold frequency?

G1 Physics · Accepted Answer

Write Einstein equations: hν = W + eVₛ/2 and hν/2 = W + eVₛ. Eliminating eVₛ gives W = (3/2)hν, hence ν₀ = 3ν/2 (option D). However ν₀ > ν, so neither incident frequency could actually cause emission. The source data are physically inconsistent. Source arithmetic leads option D but must not be published without correction.