Physics > Waves > Introduction to light

What is light?

Light behaves sometime as waves, sometime as particles. This is very strange indeed, and it is dealt with by quantum mechanics (a modern physics theory). On the same manner, very small particles, like electrons, can also behave like particle or waves. The wavelike behaviour of electrons is exploited, for instance , in electronic microscopes where beams of electrons substitute beams of light.

The particle aspect of light was demonstrated by Einstein at the beginning of the 20th century. Particles of light are called photons.

In this course we will study features of light that include both aspects: particle and wave.

Light as a wave:

Light is an electromagnetic wave, consisting of perpendicular electric and magnetic fields. Maxwell, one of the the great ENglish physiscsts of the 18th century, described such a wave using his famous equations and calculated what would be the speed of such a wave. The result was intringuing : 300 000 km/s. The same as the speed of light that ghad already been measured by a very clever device. Because of this coincicende , MAxwell concluded that hios wave was light! Fibnally the mistery of light was conquered.

What we call light is a small portion of the electromagnetic spectrum. By varying th frequency of this wave, we get a whole spectrum from radfioawaves to gamma rays Check out the EM spectrum

Diffraction is a phenomenon observed only on wave optics. Interference is another phenomenon very typical of waves..

Refraction and reflection are phenomena that can be studied in both aspects of light, but are better understood in the particle aspect, as explained below, in the form of light rays.

Diffraction occurs when light interact with objects and gaps of the same order of its wavelength (which is extremely small- of the order of a few hundred nanometres).

When light interacts with objects that are orders of magnitude larger that its wavelengths, it is best understood in terms of light rays. Those consist of particles moving in straight lines until they hit some object, causing reflection or refraction (or both).

So , I separated this course n 2 sections:

wave optics : diffraction and interference

ray optics : reflection and refraction