InterviewSolution
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InterviewSolution
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18. A small metal plate (work function = 1.17 eV) isplaced at a distance of 2 m from a monochromaticlight source of wavelength 4.8 x 107 m and power20 watt. The light falls normally on the plate. Thenumber of photons striking the metal plate persecond per sq metre area will be: (h 6-6 x 10-34 Js)(a) 9.64 x 1018(c) 9.64 x 1016(b) 9.64 x 1017(d) 9.64 x 1015mum kinetic enerov |
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Answer» Suppose the source emits n photons of frequency f per second. Therefore , n hf = nh(c/Lambda)=20J. ( Because a 20W source emits 20J energy per second). Therefore, n=[20x 4.8x10^-7]/[(6.62x10^-34)(3.0x10^8)]=4.8338x10^19 This number of photons are incident on the spherical surface of radius of 2 m per second . Hence, the number of photons arriving on unit area per second will be 4.8338x10^19/[4 pi 2^2]=4.8338x10^19/(16x3.14)=0.096x10^19=9.6x10^17 photons per meter square per second hence, correct option is (b) |
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