2.48    In astronomical observations, signals observed from the distant stars are generally weak. If the photon detector receives a total of 3.15\times 10^{-18}\ \textup{J} from the radiations of 600 nm, calculate the number of photons received by the detector.

Answers (1)

Let the number of photons received by the detector be 'N'.

Then, the total energy it receives from the radiation of 600 nm will be:

E=Nh\nu = N\frac{hc}{\lambda}    Or   N = \frac{\lambda E}{hc}

Where, 

\lambda = 600\ nm = 600\times10^{-9}m,

E = 3.15\times10^{-18}J,

h = 6.626\times10^{-34}Js  and  c = 3.0\times10^8 m/s

Substituting the values in the equation above, we get

N = \frac{(3.15\times10^{-18}J)\times(600\times10^{-9}m)}{(6.626\times10^{-34}Js)\times(3.0\times10^8m/s)}

= 9.51 \approx 10  number of photons is received by the detector.

 

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