The energy of photon is given by E=λhc.
Power(P) is given as, P=tE=λtnhc
From the above equation, the number of photons is n=hcPλt
=0.5×103×6.6×10−34×3×108660×10−9×60×10−3
Hence, number of photons in the pulse are=100×1018=1020.
JEE Main 2017 — Physics Modern Physics
A laser light of wavelength 660nm is used to weld Retina detachment. If a laser pulse of width 60ms and power 0.5kW is used, the approximate number of photons in the pulse are (Take Planck's Constant, h=6.62×10−34Js)
Held on 9 Apr 2017 · Verified 6 Jul 2026.
1022
1019
1020
1018
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