In a photoemission experiment, the maximum kinetic energies of photoelectrons from metals P , Q and R are E P , E Q and E R , respectively, and they are related by E P = 2 E Q = 2 E R . In this experiment, the same source of monochromatic light is used for metals P and Q while a different source of monochromatic light is used for the metal R . The work functions for metals P , Q and R are 4 . 0 eV , 4 . 5 eV and 5 .

Step-by-step solution

Let the maximum kinetic energies of photoelectrons be E P = 2 E Q = 2 E R = 2 E . The energy of incident photon on metal P   and   Q be U and for R be U ' . Photoelectric equation, E ph = ϕ + K E max Now, using it for the three cases, U = 4 + 2 E       . . . 1 U = 4 . 5 + E       . . . 2 U ' = 5 . 5 + E       . . . 3 From 1   and   2 , E = 0 . 5   eV From 3 , energy of the incident photon for metal R , U ' = 5 . 5 + 0 . 5 = 6