A Laser light of wavelength 660,nm is used to weld Retina detachment. If a Laser pulse of width 60,

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11.Dual Nature of Radiation and matter

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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 $h\, = 6.62\times10^{- 34}\, Js$]

A

$10^{20}$

B

$10^{18}$

C

$10^{22}$

D

$10^{19}$

(JEE MAIN-2017)

Solution

Given, $\lambda=660 \mathrm{nm}, \text { Power }=0.5 \mathrm{kW}, \mathrm{t}=60 \mathrm{ms}$

Power $P=\frac{\text { nhc }}{\lambda t} \Rightarrow n=\frac{p \lambda t}{h c}$

$=0.5 \times 10^{3} \times $ $\frac{{660 \times {{10}^{ – 9}} \times 60 \times {{10}^{ – 3}}}}{{6.6 \times {{10}^{ – 34}} \times 3 \times {{10}^8}}}$

$=100 \times 10^{18}=10^{20}$

Standard 12

Physics

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