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Sun light falls normally on a surface of area 36 cm 2 and exerts an average force of 7.2 × 10 –9 N within a time period of 20 minutes. Considering a case of complete absorption, the energy flux of incident light is

1. 25.92 × 10 2 W/cm 2
2. 8.64 × 10 –6 W/cm 2
3. 6.0 W/cm 2
4. 0.06 W/cm 2

Correct answer: 0.06 W/cm 2

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