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Sunlight 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 ______.

#### Options

25.92 × 10

^{2 }W/cm^{2}8.64 × 10

^{-6 }W/cm^{2}6.0 W/cm

^{2}0.06 W/cm

^{2}

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#### Solution

Sunlight 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 **0.06 W/cm ^{2}**.

**Explanation:**

`"I"/"C"xx"area"` = force

⇒ `"I"/"C"xx36xx10^-4 = 7.2 xx 10^-9`

⇒ I = `(7.2xx10^-9xx3xx10^8)/(36xx10^-9xx10)=(6xx10^-1)/10^-3`

⇒ I = 6 × 10^{2 }`"W"/"m"^2`

⇒ I = 0.06 `"W"/"cm"^2`

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