Dual Nature of Matter

JEE Main level, single correct, medium

179 of 200

Question 179 of 200

A laser light of wavelength 660nm660nm is used to weld Retina detachment. If a laser pulse of width 60ms60ms and power 0.5kW0.5kW is used, the approximate number of photons in the pulse are (Take Planck's Constant, h=6.62×10−34Js)h=6.62\times {10}^{-34}Js)

Show answer and solution

Answer: (C) 1020{10}^{20}

The energy of photon is given by E=hcλE=\dfrac{hc}{\lambda }.
Power(P)\left(P\right) is given as, P=Et=nhcλtP=\dfrac{E}{t}=\dfrac{nhc}{\lambda t}
From the above equation, the number of photons is n=Pλthcn=\dfrac{P\lambda t}{hc}

=0.5×103×660×10−9×60×10−36.6×10−34×3×108=0.5\times {10}^{3}\times \dfrac{660\times {10}^{-9}\times 60\times {10}^{-3}}{6.6\times {10}^{-34}\times 3\times {10}^{8}}

Hence, number of photons in the pulse are=100×1018=1020=100\times {10}^{18}={10}^{20}.

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.
See it move: Photoelectric effect and matter waves simulationDrag the sliders and watch the numbers in this question change.Revise Modern Physics firstFormula sheet, solved examples and the traps students fall into.

More Physics practice

JEE Main Physics practice question on Dual Nature of Matter (Photoelectric Effect), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.