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

The force exerted on the cardboard by the light is
`1.2* 10^(-11)\ N`

Step-by-step 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=(I)/(c)`...........(1)

c is the speed of light

The relation between force and pressure is given by :

`P=(F)/(A)`.......(2)

From equation (1) and (2):

`F=(IA)/(c)`

`F=(18\ W/m^2* 0.0002\ m^2)/(3* 10^8\ m/s)`

`F=1.2* 10^(-11)\ N`

So, the force exerted on the cardboard by the light is
`1.2* 10^(-11)\ N`. Hence, this is the required solution.