Question #1: Photoelectric effect (6 pts): The cathode is hit by monochromatic l

Question

Question #1: Photoelectric effect (6 pts): The cathode is hit by monochromatic light of 5 eV photon energy (UV light).

a) (3 pts) What is the wavelength of the light (hint: blue light has a wavelength of about 400 nm, i.e. the solution needs to yield a shorter wavelength)?
(All you need: E=hv, c= (lambda)(v); h=6.62E-34 Js, e=1.602E-19 C, c=3E8 m/s); Please, indicate if you use the back of the sheet for your calculations.


b) (3 pts) Assuming the work function (energy needed to extract an electron into the vacuum) of the cathode is 4 eV, what is the minimum counter potential V that needs to be applied in order to suppress the current?

Answer: V =

Explanation / Answer

a)

5* 1.6*10^-19 = hc/

= 248 nm

b)

4+5 = 9 eV

so 9 V

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