Dual Nature of Matter

JEE Main level, single correct, medium

170 of 200

Question 170 of 200

A 2mW2mW laser operates at a wavelength of 500nm500nm . The number of photons that will be emitted per second is:
[Given Planck's constant h=6.6×10−34Js,h=6.6\times {10}^{-34}Js, speed of light c=3.0×108m/sc=3.0\times {10}^{8}m/s ]

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Answer: (B) 5×10155\times {10}^{15}

P=2mWP=2 mW
λ=500nm\lambda =500 nm
Number of photons will be emitted per second is,
n=P(hcλ)=2×10−3×500×10−96.6×10−34×3×108n=\dfrac{P}{\left(\dfrac{hc}{\lambda }\right)}=\dfrac{2\times {10}^{-3}\times 500\times {10}^{-9}}{6.6\times {10}^{-34}\times 3\times {10}^{8}}
=5×1015=5\times {10}^{15}

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