Q130 / 270 · NDA 2020 · General Ability

Light of uniform intensity impinges perpendicularly on a totally reflecting surface. If the area of the surface is halved, the radiation force on it will become

  • A
    double
  • Correct answer
    B
    half
  • C
    four times
  • D
    one fourth

Solution

We know that force, $\mathrm{F}=\frac{\Delta p}{\Delta t}=\frac{2 I A}{C}$ Here, I $=$ Intensity of light falling on the surface $\mathrm{C}=$ Speed of light $A=$ Area of surface. If $A$ is halved, then $\mathrm{F}=\frac{2 I \frac{A}{2}}{C}=\frac{I A}{C}$ Thus, Force becomes half.

Hence, the correct answer is option: 'B'.

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