Number of photons of equal energy emitted per second by a 6 mW laser source operating at 663 nm is $\_\_\_\_$ .
(Given : $\mathrm{h}=6.63 \times 10^{-34} \mathrm{~J}. \mathrm{s}$ and $\mathrm{c}=3 \times 10^{8} \mathrm{~m} / \mathrm{s}$ )

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Number of photons of equal energy emitted per second by a 6 mW laser source operating at 663 nm is \_\_\_\_ . (Given : h=6.63 × 10^ -34 ~J. s and c=3 × 10^ 8 ~m / s )

Quantrex Academy · Accepted Answer

Correct answer: A. 2 × 10^ 16

Power of laser: P = 6 mW = 6 × 10^ -3 J/s Energy of a single photon at wavelength λ = 663 nm: E = h = (hc)/(λ) = 6.63 × 10^ -34 × 3 × 10^8 663 × 10^ -9 E = (6.63 × 3)/(663) × 10^ -34+8+9 = (19.89)/(663) × 10^ -17 = 3 × 10^ -19 J Number of photons emitted per second: N = Total Energy per second Energy per photon = 6 × 10^ -3 3 × 10^ -19 = 2 × 10^ 16

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