Electromagnetic Waves

JEE Main level, numerical answer, medium

83 of 165

Question 83 of 165

If 2.5×10−6N2.5\times {10}^{-6}N average force is exerted by a light wave on a non-reflecting surface of 30cm230{cm}^{2} area during 40min⁡40\min of time span, the energy flux of light just before it falls on the surface is _______ Wcm−2.W{cm}^{-2}.(Round off to the Nearest Integer), (Assume complete absorption and normal incidence conditions are there)

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Answer: 25

F=IAcF=\dfrac{IA}{c}
⇒I=FcA=2.5×10−6×3×10830=25Wcm−2\Rightarrow I=\dfrac{Fc}{A}=\dfrac{2.5\times {10}^{-6}\times 3\times {10}^{8}}{30}=25W{cm}^{-2}

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