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(A) The power of the laser source is $P = 5 	imes 10^{-3} \,W$. The time duration is $t = 2 \,s$. The wavelength is $\lambda = 632.2 	imes 10^{-9} \

Vedclass · Accepted Answer

$3.2$

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(A) The power of the laser source is $P = 5 	imes 10^{-3} \,W$. The time duration is $t = 2 \,s$. The wavelength is $\lambda = 632.2 	imes 10^{-9} \,m$.The total energy emitted in time $t$ is $E_{total} = P 	imes t = 5 	imes 10^{-3} 	imes 2 = 10^{-2} \,J$.The energy of a single photon is $E_{photon} = \frac{hc}{\lambda} = \frac{6.63 	imes 10^{-34} 	imes 3 	imes 10^8}{632.2 	imes 10^{-9}} \,J$.$E_{photon} = \frac{19.89 	imes 10^{-26}}{632.2 	imes 10^{-9}} \approx 0.03146 	imes 10^{-17} \,J = 3.146 	imes 10^{-19} \,J$.The number of photons $n$ is given by $n = \frac{E_{total}}{E_{photon}} = \frac{10^{-2}}{3.146 	imes 10^{-19}} \approx 0.3178 	imes 10^{17} = 3.178 	imes 10^{16}$.Rounding to the nearest provided option,the value is $3.2 	imes 10^{16}$.

How many photons are emitted by a laser source of $5 \times 10^{-3} \,W$ operating at $632.2 \,nm$ in $2 \,s$? The answer is $....... \times 10^{16}$. (Given: $h = 6.63 \times 10^{-34} \,Js$,$c = 3 \times 10^8 \,m/s$)

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