A photoelectric experiment indicates that violet light of wavelength 420 nm is the longest wavelength radiation that can cause photoemission

Question

A photoelectric experiment indicates that violet light of wavelength 420 nm is the longest wavelength radiation that can cause photoemission of electrons from a particular multi alkali photocathode surface.
(a) What is the work function of the photocathode surface, in eV?
(b) If a UV radiation of wavelength 300 nm is incident upon the photocathode surface, what will be the maximum kinetic energy of the photo emitted electrons, in eV?

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Thanh Hà 4 years 2021-08-19T03:58:50+00:00 1 Answers 72 views 0

Answers ( )

  1. Philomena
    0
    2021-08-19T04:00:02+00:00
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    Answer:

    (a). The formula for the photoelectric effect is

    Ef = W + Ek

    where

    Ef = photon energy.

    W = work function.

    Ek = kinetic energy of an electron ripped of a metal

    In this case the electron does not have kinetic energy, Ek = 0. Hence

    Ef = W

    But  Ef = hv (h: Planck constant, v: frequency of the photon)

    We can calculate the photon energy by taking into account the wave length and spped of the ligth

    Ef = hv = hc/λ = 6.62*10^(-34)*3*10^(8)/(420*10^(-9)) = 4.72*10^(-19) J

    But in eV

    Ef =  4.72*10^(-19)*6.24*10^(18) = 2.94 eV

    (b). Ek = Ef – W = hc/λ – W

        Ek = 6.62*10^(-34)*3*10^(8)/(300*10^(-9)) J – 2.94 eV

        Ek = 6.62*10^(-19)*6.24*10^(18) eV – 2.94 eV

        Ek = 1.19 eV

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