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(A) Given: Wavelength $\lambda = 660\,nm = 660 	imes 10^{-9}\,m$,Power $P = 0.5\,kW = 0.5 	imes 10^3\,W$,Pulse width $t = 60\,ms = 60 	imes 10^{-3}

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$10^{20}$

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(A) Given: Wavelength $\lambda = 660\,nm = 660 	imes 10^{-9}\,m$,Power $P = 0.5\,kW = 0.5 	imes 10^3\,W$,Pulse width $t = 60\,ms = 60 	imes 10^{-3}\,s$,Planck's constant $h = 6.62 	imes 10^{-34}\,Js$,Speed of light $c = 3 	imes 10^8\,m/s$.The total energy $E$ of the pulse is given by $E = P 	imes t$.The energy of a single photon is $E_{photon} = \frac{hc}{\lambda}$.The number of photons $n$ is given by $n = \frac{E}{E_{photon}} = \frac{P 	imes t 	imes \lambda}{h 	imes c}$.Substituting the values:$n = \frac{0.5 	imes 10^3 	imes 60 	imes 10^{-3} 	imes 660 	imes 10^{-9}}{6.62 	imes 10^{-34} 	imes 3 	imes 10^8}$.Approximating $6.62 \approx 6.6$:$n = \frac{0.5 	imes 60 	imes 660 	imes 10^{-9}}{6.6 	imes 3 	imes 10^{-26}} = \frac{30 	imes 660 	imes 10^{-9}}{19.8 	imes 10^{-26}} \approx \frac{19800 	imes 10^{-9}}{19.8 	imes 10^{-26}} \approx 1000 	imes 10^{17} = 10^{20}$.Thus,the number of photons is $10^{20}$.

$A$ Laser light of wavelength $660\,nm$ is used to weld Retina detachment. If a Laser pulse of width $60\,ms$ and power $0.5\,kW$ is used,the approximate number of photons in the pulse are: [Take Planck's constant $h = 6.62 \times 10^{-34}\,Js$]

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