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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.

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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.

 

Posted by

Divya Prakash Singh

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