Electromagnetic Waves

JEE Main level, single correct, medium

57 of 165

Question 57 of 165

Sun light falls normally on a surface of area 36cm236{cm}^{2} and exerts an average force of 7.2×10−9N7.2\times {10}^{-9}N within a time period of 2020 minutes. Considering a case of complete absorption, the energy flux of incident light is

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Answer: (D) 0.06Wcm−20.06W{cm}^{-2}

The radiation pressure in case of complete absorption is given by,
P=IcP=\dfrac{I}{c}.
Therefore, the force will be,
F=Ic×A⇒I=FcAF=\dfrac{I}{c}\times A \Rightarrow I=\dfrac{Fc}{A}
⇒I=7.2×10−9×3×10836×10−4=600Wm−2⇒I=0.06Wcm−2\Rightarrow I=\dfrac{7.2\times {10}^{-9}\times 3\times {10}^{8}}{36\times {10}^{-4}}=600W{m}^{-2} \Rightarrow I=0.06W{cm}^{-2}

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