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NCERT Class XI Chemistry Structure of Atom Solutions

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Question : 48 of 67
Marks: +1, -0
In astronomical observations, signals observed from the distant stars are generally weak. If the photon detector receives a total of 3.15 × 10−18J10^{-18} \mathrm{J} from the radiations of 600 nm, calculate the number of photons received by the detector.
Solution:  
Energy of photon, E = hcλ\frac{hc}{\lambda},
Here, h = 6.626 × 10−34Js10^{-34} \mathrm{Js}, c = 3 × 108m s−110^{8} \mathrm{m\,s^{-1}}, λ = 600 nm = 600 × 10−9m10^{-9} \mathrm{m} = 6 × 10−7m10^{-7} \mathrm{m}
∴ E = 6.626×10−34×3×1086×10−7\frac{6.626 \times 10^{-34} \times 3 \times 10^{8}}{6 \times 10^{-7}} = 3.31 × 10−19J10^{-19} \mathrm{J}
Since Total energy received = 3.15 × 10−1810^{-18} J
Number of photons = 3.15×10−183.31×10−19\frac{3.15 \times 10^{-18}}{3.31 \times 10^{-19}} = 9.52 ≈ 10
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