NCERT Book Class 12 Physics Chapter 10 Wave Optics

Wave Optics

Chapter Ten

WAVE OPTICS

10.1 INTRODUCTION
In 1637 Descartes gave the corpuscular model of light and derived Snell’s
law. It explained the laws of reflection and refraction of light at an interface.
The corpuscular model predicted that if the ray of light (on refraction)
bends towards the normal then the speed of light would be greater in the
second medium. This corpuscular model of light was further developed
by Isaac Newton in his famous book entitled OPTICKS and because of
the tremendous popularity of this book, the corpuscular model is very
often attributed to Newton.
In 1678, the Dutch physicist Christiaan Huygens put forward the
wave theory of light – it is this wave model of light that we will discuss in
this chapter. As we will see, the wave model could satisfactorily explain
the phenomena of reflection and refraction; however, it predicted that on
refraction if the wave bends towards the normal then the speed of light
would be less in the second medium. This is in contradiction to the
prediction made by using the corpuscular model of light. It was much
later confirmed by experiments where it was shown that the speed of
light in water is less than the speed in air confirming the prediction of the
wave model; Foucault carried out this experiment in 1850.
The wave theory was not readily accepted primarily because of
Newton’s authority and also because light could travel through vacuum 255