Ram knows that red light has greater intensity and so it is much bright but in case of photoelectric emission it cannot produce the emission of electrons from a clean zinc surface, while even weak ultraviolet radiation can do so. He could not know specific cause of such thing. Then he went to his friend Shyam for its specific explanation. Shyam explained him that the photo emission of electron does not depend on the intensity while it depends on the frequency and thus on the energy of photon of incident light. The energy of photon of red light is less than the work function of zinc, so red light cannot emit photoelectrons. Similarly, the energy of photon of ultraviolet light is greater than the work function of zinc, so ultraviolent light can emit photoelectrons.
(a) What values are noticed in Shyam ?
(b) The work functions of lithium and copper are 2.3 eV and 4 eV respectively. Which of these metals are useful for the photoelectric cell working with visible light ? Explain.