A low intensity ultraviolet light of wavelength `2271Å` irradiates a photocell made of molybdenum metal. If the stopping potential is 1.3V, find the work function of the metal. Will the photocell work if it is irradiated by a high intensity red light of wavelength `6328Å` ?

Explanation

The energy of eV of incident photons is
`E = ( 12431)/( 2271) eV = 5.47eV`
As stopping potential for ejected electrons is 1.3 V, the maximum kinetic energy of ejected electrons will be `KE_("max") = eV_(0) = 1.3 eV`
Nowfrom photoelectric effect equation, we have
`E = phi + KE_("max")`
or `phi= E- KE_("max")`
or `phi= 5.47 - 1.3 eV= 4.17 eV`
Energy in eV for photons for red light wavelength `6328Å`
`E' = ( 12431) /( 6328) eV= 1.96eV `
As` E' lt phi`, photocell will not work if irradiated by this red no matter however intense the light will be.