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JEE Main 2017 · 9 Apr · Shift 1, Physics question 24

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=6.62×10−34h=6.62\times10^{-34} Js]

Choose one option
Answer and worked solution

Official answer: A

N=Ptλhc=500×0.06×660×10−96.62×10−34×3×108≈1.0×1020.N=\frac{Pt\lambda}{hc}=\frac{500\times0.06\times660\times10^{-9}}{6.62\times10^{-34}\times3\times10^8}\approx1.0\times10^{20}.

Topics:Photoelectric effect
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