Sodium has a work function of 2.46 eV.
(a) Find the cutoff wavelength and cutoff frequency for the photoelectric effect.
(b) What is the stopping potential if the incident light has a wavelength of 168 nm?
(a) As given work function = 2.46 eV = 2.46 x 1.6 x 10-19 J
Work function = 3.936 x 10-19 J
Photon must have at least this much energy for knocking out an electron.
Hence, hf = 3.936 x 10-19
h = planks const
f = frequency
f = 3.936/6.64 x 10-19+34
f = 5.927 x 1014 Hz (this is required cut off frequency)
As lambda = c/f = 3.0/5.927 x 108-14
lambda = 5.06 x 10-7 m (which is required cut of wavelength)
(b) energy of incedent photon E = hc/lambda =( 6.64 x 3 / 168 ) x 10-34+8+9
E = 1.185 x 10-18 J
As elenrgy of electron will be Ee = (11.85 - 3.936) x 10-19 = 8.484 x 10-19 J
As this must be equal to energy of electron in potential,
Ee = eV
V = Ee/e = 8.454 x 10-19/1.6 x 10-19 V
V = 5.28375 Volt
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