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

Question

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

MARKS App · Accepted Answer

Energy of one photon $=h v=h \frac{\mathrm{c}}{\lambda}$ $=\frac{\left(6.626 \times 10^{-34} \mathrm{Js}\right)\left(3 \times 10^8 \mathrm{~ms}^{-1}\right)}{\left(600 \times 10^{-9} \mathrm{~m}\right)}=3.313 \times 10^{-19} \mathrm{~J}$ Total energy received $=3.15 \times 10^{-18} \mathrm{~J}$ $\therefore$ No. of photons received $=\frac{3.15 \times 10^{-18}}{3.313 \times 10^{-19}}=9.51=10$

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