PHYS 2212 Module 12.4

Momentum and Radiation Pressure

Recommended Reading

12.4 Momentum and Radiation Pressure

Learning Objectives

By the end of this section, you will be able to:

  • Describe the relationship of the radiation pressure and the energy density of an electromagnetic wave
  • Explain how the radiation pressure of light, while small, can produce observable astronomical effects

Radiation Pressure


Sunlight falls with an intensity of 500 W/m^2 on this sheet of paper, which reflects 80% of it.

What force does the light exert on the paper?

A 17.0 mW helium-neon laser (λ = 632.8 nm) emits a beam of circular cross section with a diameter of 2.00 mm.

(a) Find the maximum electric field in the beam. 

(b) What total energy is contained in a 3.00 m length of the beam?

(c) Find the momentum carried by a 3.00 m length of the beam.