Concepts Of Physics MCQ Edition [Volume 2]PhysicsPhotoelectric Effect and Wave–Particle Duality
A 100 W light bulb is positioned at the centre of a spherical chamber having a radius of 20 cm . Assuming that 60 % of the energy supplied to the bulb is converted into light and the chamber's surface is perfectly absorbing, determine the pressure exerted by the light on the surface of the chamber.
Options
- A4.0 10⁻⁷ Pa
- B8.0 10⁻⁷ Pa
- C1.6 10⁻⁶ Pa
- D6.6 10⁻⁷ Pa
Correct answer
A. 4.0 10⁻⁷ Pa
Step-by-step solution
Power of the light emitted, P = 60 % of 100 W = 60 W Radius of the spherical chamber, r = 20 cm = 0.2 m Intensity of light at the surface of the chamber is given by: I = P 4 r^2 For a perfectly absorbing surface, the radiation pressure p is: p = I c = P 4 r^2 c Substituting the given values: p = 60 4 (0.2)^2 3 10^8 p = 60 4 0.04 3 10^8 p = 60 0.48 10^8 p = 125 10⁻⁸ Pa p 39.8 10⁻⁸ Pa = 3.98 10⁻⁷ Pa 4.0 10⁻⁷ Pa