Abstract: The paper begins with a brief account of classical theory of radiation and its failure to explain black body radiation. It is followed by the introduction of Quantum Theory of radiation by Max Planck. The dual nature of matter by de Broglie has been extensively dealt with. The uncertainty principle of Heisenberg has been critically discussed by many eminent authors who finally concluded it as one of the unavoidable mysteries of nature. As a picture speaks thousand words and as face is the index of the mind, the author has added pictures of eminent physicists at appropriate places. The subject matter of the paper will form a good text for any graduate students of Physics.
Keywords: Classical theory, Dual nature, Photon, Planck’s constant, Quantum Theory, Schrodinger equation, Ultraviolet catastrophe, Uncertainty principle, Wave mechanics.