If 2.5 × 10 - 6 N average force is exerted by a light wave on a… | JEE Main 2021 (17 Mar, Shift 1)

Q9JEE Main 2021 · 17 MAR · SHIFT 1Medium

Momentum & Radiation Pressure

If 2.5 $\times$ 10 $-$ 6 N average force is exerted by a light wave on a non-reflecting surface of 30 cm2 area during 40 minutes of time span, the energy flux of light just before it falls on the surface is ___________ W/cm2. (Round off to the Nearest Integer)

(Assume complete absorption and normal incidence conditions are there)

Numerical answer type. Work it out, then open the answer.

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Answer: 25

Complete absorption: $F = \dfrac{IA}{c} \Rightarrow I = \dfrac{Fc}{A}$
$I = \dfrac{2.5 \times 10^{-6} \times 3 \times 10^8}{30\ \text{cm}^2} = \dfrac{750\ \text{W}}{30\ \text{cm}^2}$
$I = 25\ \text{W/cm}^2$

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