Question

Sunlight falls normally on a surface of area 36 cm² 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 × 10² W/cm²  

• 8.64 × 10^-6 W/cm²  

• 6.0 W/cm²  

• 0.06 W/cm²  

Answer 1

Sunlight falls normally on a surface of area 36 cm² 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/cm².

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 × 10² `"W"/"m"^2` 

⇒ I = 0.06 `"W"/"cm"^2`