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QJEEM17Phc976: JEE Main 2017 Physics - Class 12 JEEM17Phc976 Solution: A Laser light of wavelength 660 nm is used to weld Retina…

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]

Multiple Choice Options

  • A 1020
  • B 1018
  • C 1022
  • D 1019

Step-by-Step Verified Solution

The power of the given laser light is expressed as

P=nhcλtP = {{nhc} \over {\lambda t}}

from which the number of photons per second is given by

n=P(λthc)=(5×102)×[(660×10−9)(60×10−3)(6.6×10−34)(3×108)]n = P\left( {{{\lambda t} \over {hc}}} \right) = (5 \times {10^2}) \times \left[ {{{(660 \times {{10}^{ - 9}})(60 \times {{10}^{ - 3}})} \over {(6.6 \times {{10}^{ - 34}})(3 \times {{10}^8})}}} \right]

=100×1018=1020= 100 \times {10^{18}} = {10^{20}}

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