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AIIMS 2009
Exam
AIIMS
Year
2009
Subject
Physics
Chapter
Thermal Properties of Matter

AIIMS 2009 · Physics · Thermal Properties of Matter

Light with an energy flux of 18 ~W / cm^2 falls on a non-reflecting...

Light with an energy flux of 18 W/cm218 \mathrm{~W} / \mathrm{cm}^2 falls on a non-reflecting surface at normal incidence. The pressure exerted on the surface is

Options

  1. A2 N/m22 \mathrm{~N} / \mathrm{m}^2
  2. B2×10−4 N/m22 \times 10^{-4} \mathrm{~N} / \mathrm{m}^2
  3. C6 N/m26 \mathrm{~N} / \mathrm{m}^2
  4. D6×10−4 N/m26 \times 10^{-4} \mathrm{~N} / \mathrm{m}^2

Correct answer

D. 6×10−4 N/m26 \times 10^{-4} \mathrm{~N} / \mathrm{m}^2

Step-by-step solution

Radiation pressure Prad P_{\text{rad }} due to light falling on a non-reflecting surface at normal incidence is given by Prad = Energy flux  Speed of light =18W/cm23×108m/s=18×104W/m23×108m/s=6×10−4N/m2\begin{aligned} & P_{\text{rad }}=\frac{\text{ Energy flux }}{\text{ Speed of light }}=\frac{18 \mathrm{ W} / \mathrm{cm}^2}{3 \times 10^8 \mathrm{ m} / \mathrm{s}} \\ & =\frac{18 \times 10^4 \mathrm{ W} / \mathrm{m}^2}{3 \times 10^8 \mathrm{ m} / \mathrm{s}}=6 \times 10^{-4} \mathrm{ N} / \mathrm{m}^2\end{aligned}
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