Q.

A monochromatic infrared range finder of power 1mW emits photons with wavelength 1000 nm in 0.1 seconds. The number of photons emitted in 0.1 seconds is
(Given h =6.626×10-34) Js, c=3×108 ms-1, Avogadro number =6.022×1023)

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a

5 x 1014

b

5 x 1011

c

30 x 1034

d

30 x 1037

answer is A.

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Detailed Solution

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(P) Power =1 mW=103 watt
E=P×t=103×0.1=102
λ=1000 nm=106
We know,
E=nhv 
Here, E= Energy of n photons
n= number of photons
hu = energy of 1 photon
E=n×hcλn=hc=104×1066.625×1034×3×108=1066.625×3=0.05×106=5×1014

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A monochromatic infrared range finder of power 1mW emits photons with wavelength 1000 nm in 0.1 seconds. The number of photons emitted in 0.1 seconds is(Given h =6.626×10-34) Js, c=3×108 ms-1, Avogadro number =6.022×1023)