#### 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

#### 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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Solution 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 Concept: Particle Nature of Electromagnetic Radiation: Planck'S Quantum Theory.