Your last submission is used for your score. 2 points Tpler6 21.P025. My Notes A

Question

Your last submission is used for your score. 2 points Tpler6 21.P025. My Notes Ask Your Teac 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 +1.53 nC if 1.01 x 1o6 electrons are ejected per second? (b) If 1.37 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.)

Explanation / Answer

Given,

Q = 1.53 nC ; q/t = 1.01 x 10^6 electrons/s

We know from the defination of current:

I = Q/t

t = Q/I ; I = dq/dt

t = 1.53 x 10^-9/(1.01 x 10^6 electron/s)(1.6 x 10^-19 C/electron) = 9.47 x 10^3 s

t = 9.47 x 10^3 s = 9.47 x 10^3 s x 1 hr/3600 s = 2.63 hr

Hence, t = 2.63 hr

b)E = 1.37 eV

We know from the defination of power,

P = dE/dt ;

dE = E I dt

P = E I t/dt = E I

P = 1.37 eV x 10.6 x 10^-19 J/eV x 1.01 x 10^6 electrons/s = 2.21 x 10^-13 W

Hence, P = 2.21 x 10^-13 W

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