A 100 W light bulb is placed at the centre of a spherical chamber of radius 20cm. Assume that 60% of the energy supplied to the bulb is converted into light and that the surface of the chamber is perfectly absorbing. Find the pressure exerted by the light on the surface of the chamber.

Explanation

` Power = 100 W , radius = 20 cm`
60% is converted to light = 60 W
Now, Force = power / Velocity
` = 60 / 3 xx 10^(8) = 2 xx 10^(-7) N `
`Pressure = Force / Area `
` = 2 xx 10^(-7) / 4 xx 3.14 xx (0.2)^(2) `
`= 1 /8 xx 3.14 xx 10^(-5)`
` 0.039 xx 10^(-5) `
`= 3.9 xx 10^(-7)`
` = 4 xx 10^(-7) N / m^(2)`.