We know that light is a form of energy and it travels in the form of electromagnetic waves. These waves are made up of electrical and magnetic vectors which are perpendicular to each other and also to the direction of propagation. The electro-magnetic theory of light was propounded by a physicist Maxwell. This was a very comprehensive theory, but yet could not explain certain phenomena of physics.
We know that red hot objects usually emit red light. The frequency of this light does not depend upon the substance which is being heated up but upon the temperature of the substance. Efforts were made to establish a relationship between temperature and frequency on the basis of electromagnetic theory. But, the theory failed to explain the frequencies of ultraviolet light.
However, this problem was solved in 1900 by a German physicist, Max Karl Planck. He suggested that light is emitted in bundles or packets instead of a steady stream. And this packet of light was called quantum. The contention put forth by Planck is now known as the Quantum Theory. According to this theory the energy of each quantum is proportional to its frequency.
In 1905 Quantum Theory solved another problem of photoelectric effect. It enabled the famous German physicist, Albert Einstein to put forward his theory of photoelectric effect. He named the light quantum as photon.
Later, Quantum Theory was used to explain many mysteries of atom. Today it has become possible to explain many effects of physics on the basis of quantum theory. Now physicists think of light as waves for some purposes and as quanta for other purposes. However, there is a highly respectable version of Quantum Theory developed recently by John Cramer, of University of Washington. His interpretation is simple and provides a new insight into the significance of the present research in this field.
