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Photoelectric Effect and WaveParticle Duality — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsPhotoelectric Effect and WaveParticle Duality3 Marks
Question
Calculate the number of photons emitted per second by a 10W sodium vapour lamp. Assume that 60% of the consumed energy is converted into light. Wavelength of sodium light = 590nm.
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Answer

$\text{p}=10\text{w}$$\therefore$ E in 1sec = 10J
% used to convert into photon = 60%
$\therefore$ Energy used = 6J
Energy used to take out 1 photon
$=\frac{\text{hc}}{\lambda}=\frac{6.63\times10^{-34}\times3\times10^{8}}{590\times10^{-9}}=\frac{6.633}{590}\times10^{-17}$
No. of photons used
$=\frac{6}{\frac{6.63\times3}{590}\times10^{-17}}=\frac{6\times590}{6.63\times3}\times10^{17}$
$=176.9\times10^{17}=1.77\times10^{19}$

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