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Question
In astronomical observations, signals observed from the distant stars are generally weak. If the photon detector receives a total of 3.15 × 10–18 J from the radiations of 600 nm, calculate the number of photons received by the detector.
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Solution
From the expression of energy of one photon (E),
`"E" = "hc"/lambda`
λ = wavelength of radiation
h = Planck’s constant
c = velocity of radiation
Substituting the values in the given expression of E:
`"E" = ((6.626 xx 10^(-34) " Js")(3xx10^(8) ms^(-1)))/((600xx10^(-9) " m"))`
Energy of one photon = 3.313 × 10–19 J
Number of photons received with 3.15 × 10–18 J energy
`= (3.15 xx 10^(-18) " J")/(3.313 xx 10^(-19)" J")`
= 9.5
`~~10`
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