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Dual Nature of Radiation and Matter — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsDual Nature of Radiation and Matter3 Marks
Question
A monochromatic light source of power 5mW emits 8 × 1015 photons per second. This light ejects photo electrons from a metal surface. The stopping potential for this set up is 2V. Calculate the work function of the metal.
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Answer

P = 5 × 10-3W, n = 8 × 1015 photons per second

Energy of each photon,

$\text{E}=\frac{\text{p}}{\text{n}}=\frac{5\times10^{-3}}{8\times10^{15}}=6.25\times10^{-19}\text{J}=\frac{6.25\times10^{-19}\text{J}}{1.6\times10^{-19}}\text{eV}$

$\text{E}=3.9\text{eV}$

Work function, W0 = E - V0

= (3.9 - 2)eV = 1.9eV

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