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Question
A filter transmits only the radiation of wavelength greater than 440 nm. Radiation from a hydrogen-discharge tube goes through such a filter and is incident on a metal of work function 2.0 eV. Find the stopping potential which can stop the photoelectrons.
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Solution
Wavelength of radiation coming from filter, λ = 440 nm
Work function of metal, ϕ = 2 eV
Charge of the electron, e = 1.6 × 10-9 C
Let V0 be the stopping potential.
From Einstein's photoelectric equation,
`(hc)/lamda - ø=eV_0`
Here,
h =Planck constant
c = Speed of light
λ = Wavelength of radiation
`(4.14 xx 10^-15xx3xx10^8)/(440xx10^-9)- 2eV = eV_0`
⇒ `eV_0 = ((1242)/440 - 2)eV = 0.823`
⇒ `V_0 = 0.823` Volts
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