The work functions (W₀ ) of K , Na , Li , Mg and Cu are 2.25,2.30,2.42,3.70 and 4.80 eV respectively. How many of these metals do not undergo photoelectric effect when a radiation of wavelength 450 ~nm is allowed to fall on them? (1 eV =1.602 10⁻¹⁹ ~J )

Step-by-step solution

aligned & =450 ~nm & E=h v aligned or aligned E & =h c 6.6 10⁻³⁴ Js 3 10^8 ~m / s 450 10⁻⁹ ~m E & =0.044 10⁻¹⁷ or 4.4 10⁻¹⁹ ~J E & = 4.4 10⁻¹⁹ 1.602 10⁻¹⁹ =2.74 eV & [ 1 eV =1.602 10⁻¹⁹ ] aligned Thus, K, Na and Li, which have less value of work functions (W₀ ) than the energy of striking photon (E) , so can undergo photoelectric effect when radiation of wavelength 450 ~nm is allowed to fall on them.