• Newton proposed the particle theory of light to explain reflection, refraction, and the rectilinear propagation of light
  • However, he could not explain diffraction
• Huygens’ principle states that every point on a wave front acts as a point source for secondary wavelets, which then spread out in the front of the initial wave at the same speed as the initial wave
  • The new wave front appears as a line tangent to all the wavelets

The wave theory proposed by Huygens explains reflection, refraction, and diffraction