A photon of energy 5 eV falls on a metal surface with work function 2 eV. If the photon were replaced by another of thrice the frequency, the kinetic energy of the fastest photoelectron would be
Correct: D
KE₁ = hν – φ = 5 – 2 = 3 eV. New frequency tripled → new energy = 3hν = 15 eV. KE₂ = 15 – 2 = 13 eV. Closest integral choice is 12 eV.