Wednesday, 3 July 2013

In astronomical observations, signals observed from the distant stars are generally weak.

Q-  2.48: 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.
Answer
From the expression of energy of one photon (E),

Where,
λ = wavelength of radiation
h = Planck’s constant
c = velocity of radiation
Substituting the values in the given expression of E:


E = 3.313 × 10-19 J
Energy of one photon = 3.313 × 10-19 J
Number of photons received with 3.15 × 10-18 J energy

= 9.5
≈ 10

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