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

Correct answer: (D) 0.06 W cm^(-2). The radiation pressure in case of complete absorption is given by, P=I/c. Therefore, the force will be, F=I/c×A⇒I=Fc/A ⇒I=(7.2×10^(-9)×3×10^8)/(36×10^(-4))=600 W m^(-2)⇒I=0.06 W cm^(-2)

Q75 / 90 · JEE Main 2022 (28 Jul Shift 2) · Physics

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

A
$25.92 \times 10^{2} W {cm}^{- 2}$
B
$8.64 \times 10^{- 6} W {cm}^{- 2}$
C
$6.0 W {cm}^{- 2}$
Correct answer
D
$0.06 W {cm}^{- 2}$

Solution

The radiation pressure in case of complete absorption is given by,
$P = \frac{I}{c}$ .
Therefore, the force will be,
$F = \frac{I}{c} \times A \Rightarrow I = \frac{F c}{A}$
$\Rightarrow I = \frac{7.2 \times 10^{- 9} \times 3 \times 10^{8}}{36 \times 10^{- 4}} = 600 W m^{- 2} \Rightarrow I = 0.06 W {cm}^{- 2}$

Hence, the correct answer is option: 'D'.

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Sun light 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

Solution

Relevant Questions

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