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A parallel beam of monochromatic light of wavelength 550 \mathrm{~nm} falls normally on a plane metallic surface which is perfectly reflecting. The power of the beam is 5 \mathrm{~mW} and its cross-sectional area is 1.0 \mathrm{~mm}^2. Find the force and pressure exerted by the radiation on the metallic surface:
 

Option: 1

1.65 \times 10^{-11} \mathrm{~N}, 1.65 \times 10^{-5} \mathrm{~N} / \mathrm{m}^2


Option: 2

\quad 3.3 \times 10^{-11} \mathrm{~N}, 3.3 \times 10^{-5} \mathrm{~N} / \mathrm{m}^2


Option: 3

1.65 \times 10^{-11} \mathrm{~N}, 3.3 \times 10^{-5} \mathrm{~N} / \mathrm{m}^2


Option: 4

3.3 \times 10^{-11} \mathrm{~N}, 1.65 \times 10^{-5} \mathrm{~N} / \mathrm{m}^2


Answers (1)

best_answer

As, I=\frac{P}{A}=\frac{5 \times 10^{-3}}{1 \times 10^{-6}}=5 \times 10^3 \mathrm{~W} / \mathrm{m}^2

Force on the surface, \mathrm{F}=\frac{2 \mathrm{P}}{\mathrm{c}}=\frac{2 \times 5 \times 10^{-3}}{3 \times 10^8}=3.3 \times 10^{-11} \mathrm{~N} 

Pressure on the surface, =\frac{2 \mathrm{I}}{\mathrm{c}}=\frac{2 \times 5 \times 10^{-3}}{3 \times 10^8}=3.3 \times 10^{-5} \mathrm{~N} / \mathrm{m}^2

Posted by

Pankaj

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