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NEET PHYSICSDUAL NATURE OF RADIATION AND MATTERMedium

Question

Light with an energy flux of 25×10425 \times 10^4 Wm−2^{-2} falls on a perfectly reflecting surface at normal incidence. If the surface area is 15 cm2^2, then the average force exerted on the surface is:

A

1.25×10−61.25 \times 10^{-6} N

B

2.5×10−62.5 \times 10^{-6} N

C

1.2×10−61.2 \times 10^{-6} N

D

3.0×10−63.0 \times 10^{-6} N

Step-by-Step Solution

The average force (FF) exerted by a light beam on a perfectly reflecting surface is given by the change in momentum per unit time. For a perfectly reflecting surface, the force is F=2PcF = \frac{2P}{c}, where PP is the power of the incident light and cc is the speed of light.

First, calculate the Power (PP): P=Energy Flux×AreaP = \text{Energy Flux} \times \text{Area} Given Energy Flux (II) = 25×10425 \times 10^4 W/m2^2 Area (AA) = 15 cm2=15×10−4 m215 \text{ cm}^2 = 15 \times 10^{-4} \text{ m}^2 P=(25×104)×(15×10−4)=375P = (25 \times 10^4) \times (15 \times 10^{-4}) = 375 Watts

Now, calculate the Force (FF): F=2×3753×108=7503×108=250×10−8 NF = \frac{2 \times 375}{3 \times 10^8} = \frac{750}{3 \times 10^8} = 250 \times 10^{-8} \text{ N} F=2.5×10−6 NF = 2.5 \times 10^{-6} \text{ N}

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from DUAL NATURE OF RADIATION AND MATTER. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSDUAL NATURE OF RADIATION AND MATTERenergyperfectlyreflectingsurfacenormal

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