Quantum Physics

Introduction :

In the 19th century it was realized by James Clerk Maxwell that light consists of electromagnetic waves and proposed the famous electromagnetic theory. According to the electromagnetic theory light is propagated by varying electric and magnetic fields oscillating at right angles to each other. It travels with a speed of 3 x 108 ms-1 in vacuum. It is unaffected by electric and magnetic fields, and it travels in straight lines in vacuum. It is transverse in nature and hence it may be polarized and it can exhibit interference and diffraction.

Theory of black body radiation

In the energy distribution of the spectrum of black body , the radiation emitted by black body varies with its temperature. The intensity of radiation corresponding to different wavelengths is measured at different temperatures and plotted as shown . It is observed that :

i) at a given temperature , the energy is not uniformly distributed in the radiation spectrum
ii) at a give temperature, the intensity of radiation is maximum at a particular wavelength .
iii) with increase in temperature maximum wavelength decreases
iv) for all wavelengths an incrase in temperature causes an increase in the energy emission.