A research group investigates radiation pressure using two continuous lasers that…

PHYSICS · Multi-part · CBSE · Physics · Dual Nature of Radiation and Matter · Dual Nature of Radiation and Matter

Problem

A research group investigates radiation pressure using two continuous lasers that deliver identical power

P

to identical, perfectly reflecting targets. Laser A has wavelength

\lambda_{A}=400\,\text{nm}

, and Laser B has wavelength

\lambda_{B}=800\,\text{nm}

. The beam diameters are the same, and the targets are large enough to intercept all the light. (a) Without performing detailed calculations, describe how the number of photons arriving per second depends on the laser’s wavelength when the power is held constant. (b) The average force exerted on each target is measured to be

F_{A}

for Laser A and

F_{B}

for Laser B. Explain qualitatively which force is larger and why. (c) Use proportional reasoning to determine the ratio

F_{A}/F_{B}

and justify each step of your reasoning in words.

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