Question

A black, absorbing piece of card board of area A = 2.0 cm2 absorbs light with intensity 18 W/m2. What is the force exerted on the cardboard by the light? b) 9.33x10-12 N e) 1.67x10-11 N a) 6.67x10-12 N d) 1.20x10-11 N c) 1.15x10-12 N

Answer 1

Answer:

The force exerted on the cardboard by the light is $1.2\times 10^{-11}\ N$

Explanation:

It is given that,

Area of the cardboard, $A=2\ cm^2=0.0002\ m^2$

Intensity of absorbance, $I=18\ W/m^2$

Radiation pressure in case of absorption is given by :

$P=\dfrac{I}{c}$...........(1)

c is the speed of light

The relation between force and pressure is given by :

$P=\dfrac{F}{A}$.......(2)

From equation (1) and (2):

$F=\dfrac{IA}{c}$

$F=\dfrac{18\ W/m^2\times 0.0002\ m^2}{3\times 10^8\ m/s}$

$F=1.2\times 10^{-11}\ N$

So, the force exerted on the cardboard by the light is $1.2\times 10^{-11}\ N$. Hence, this is the required solution.