Chapter 14, Problem 105A

To determine

The explanation of Huygens theory of light and Newton’s particle theory of light using the means of refraction and reflection.

Explanation of Solution

Introduction:

According to Newton’s particle theory of light, light is considered to be a “stream of particles”.

According to the Huygens' Principle, each point of wave front is a source of secondary wavelets. These wavelets spread out in every direction with the wave’s speed.

Huygens proposed theory of light and Newton proposed the particle theory of light. Comparison between both theories is mentioned below:

Newton’s particle theory of light	Huygens' Principle
Light is made up of small particles.	Every point on a wave front acts as a point source.
Explains law of reflection and refraction phenomena.	Explains law of reflection phenomena.

Newton explained reflection through his corpuscular theory by stating that light is made up of particles or corpuscles which when are incident on a rigid surface travel back at the same angle, comparing it to the motion of a perfectly elastic ball. Another proposition by Newton was that these corpuscles travel faster in denser medium due to the pull by the medium, which leads to refraction of light.

Huygens was successful in explaining reflection by stating that on reflection, the point is the source of a new wavelet which travels at an angle same as the angle of incidence. For refraction,Huygens proposed that light travelled slower in denser medium and due to this, the new wavelets travel at an angle which is the ratio of the velocities in the two media.

Both the theorists explained about the law of reflection but they differed in their explanations of theories. Huygens’ principle was able to explain the phenomenon of diffraction, interference, polarization, and also explained that reflection and refraction occurred simultaneously where Newton failed. The proposition by Newton that light travelled faster in denser medium was also disproved. Therefore, Huygens model was better at explaining reflection and refraction through wavefront model.

Conclusion:

Huygens model was better at explaining reflection and refraction through wave front model.