EM -- 114 Polarisation, Reflection and Refraction: the Phenomena

Polarisation, reflection, refraction and polarisation by reflection. We will talk about some phenomena from optics and the laws observed in those. The laws are no more empirical laws and will be derived using Maxwell’s equations in next lectures. The purpose here is to quickly recall the laws. In a wave travelling on a string, if the disturbance, or the displacement, at any point in the string is along one direction only and the same direction for all points, then we call it a polarized wave. Oscillations are along one direction only. And polarized waves can be stopped by introducing a slit which allows disturbance only in perpendicular direction. The electromagnetic waves also exhibit the phenomena of polarization. But notice, we did NOT talk about any medium. When em waves were discovered, it was assumed they were travelling through a medium called aether. Later, it was learnt that there is no aether and the waves travel in vacuum. What is oscillating about the mean position? The electric and and the magnetic fields. The waves also show phenomena of reflection and refraction. And these phenomena follow the same rules that you learnt in optics --- snell’s laws. Additionally, there is another phenomena, namely, when light (em wave) is reflected, it is polarized, partially or completely, depending on the angle of incidence. These are all observations. Enjoy.