Friday, March 2, 2012

Brief history of the nature of light

2 schools of thought concerning light

Scientists have always been puzzled by the nature of light. In the seventeenth century there were two schools of thought concerning it.


  1. Sir Isaac Newton regarded light as a stream of corpuscles or tiny particles travelling in straight lines.

  2. The Dutch physicist, Huygens, held that light consists of waves in a substance called the ether, which he supposed filled the whole of space, including that between the atoms of matter, and which could not be removed even from a vacuum.

And now,

As time went on and more became known about the behavior of light, Huygens’s wave theory came to be accepted as the better one.

At the present day, however, we have reason to believe that light consists of
stream of tiny wave-like packets of energy called photons, which travel at speed of 3 × 100000000 m/s.

Many ways to emit light

  • Atoms emit light at the temperatures produced by chemical reaction in a flame,
  • by the heating of thin tungsten wire in the ordinary electric lamp or
  • by the bombardment of gas molecules by electrons in a discharge lamp tube.

Self-luminous sources of light

 The sun and sources as described above are said to be self-luminous, since they emit light of their own accord. 

Sun. self luminated:

The common objects around us are not Self-luminous, but we are able to see them because they reflect light from the sun or other sources in all directions. Mirrors and highly polished surfaces reflect light strongly, and we shall now deal with the laws governing the reflection.

Laws of reflection of light

  1. The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.
  2. The angle of incidence is equal to the angle of reflection.

Reflection of light: