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Sodium has a work function of 2.3eV. Given that: Planck’s constant h = 6.63 x 10-34JS, velocity of light in vacuum, C = 3.0 x 108m/s, 1 electron-volt (1eV) = 1.6 x 10-19 C and mass of an electron, me = 9.1 x 10-31kg, calculate:

  1. its threshold frequency. 
  2. the maximum velocity of the photoelectrons produced when the sodium is illuminated by light of wavelength 5.0 x 10-7m.
  3. the stopping potential V, with the light of this wavelength. 

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  1. hfo = wo
    6.63 x 10-34fo=2.3 x 1.6 x10-19
    fo = 5.55 x 1014HZ
     
  2. hf = wo + 1/2MV2
    h c/λ = Wo + 1/2MV2
    6.63 x 10-34 x      3.0x108   = 2.3 x 1.6 x 10-19 + 1/2MV2
                             5.0 x 10-7
    3.978 x 10-19 = 3.68 x 10-19 + 1/2MV2
    1/2MV2 = 0.298 x 10-19
    SekphycP2A16bii
     
  3. eVs = 1/2MV2
    1.6 x 10-19Vs = 0.298 x 10-19
    Vs0.298 x 10-19
            1.6 x 10-19
    =0.186Volts

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