During a process described by the photoelectric effect, ultraviolet light can be

Question

During a process described by the photoelectric effect, ultraviolet light can be used to
charge a piece of metal.

(a) If such light is incident on a slab of conducting material and electrons are ejected with enough energy that they escape the surface of the metal, how long before the metal has a net charge of +1.55 nC if 9.90*10^5 electrons are ejected per second?

h

(b) If 1.23 eV is needed to eject an electron from the surface, what is the power rating of the light beam? (Assume this process is 100% efficient.)
W

Explanation / Answer

(a) initially metal having the net charge Q =+1.55nC
                                                             =+1.55*10-9C electrons ejected rate is R =9.90*105 electrons /s the required time is t = Q /Re 'R*e' means the amount of charge ejected /s 'e' is the charge of the electron =1.6*10-19C    t = Q /Re=1.55*10-9/9.90*105*1.6*10-19                   =0.0978535*105 s (b) energy required for eject one electron from the surface is E =1.23eV 1 eV =1.6*10-19J E =1.23*1.6*10-19J the electrons ejected rate is R =9.90*105 electrons /s that means the number of electron ejected for second are 9.90*105 the energy required for second is i.e    (power = work done /time) power rating is = E*R                         =1.23*1.6*10-19J*9.90*105                              =19.4832*10-14 W the energy required for second is i.e    (power = work done /time) power rating is = E*R                         =1.23*1.6*10-19J*9.90*105                              =19.4832*10-14 W

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