Quantum Mechanics #1- The Origin

INTRODUCTION

What is Quantum mechanics?| Quantum Mechanics is the theory which attempts to explain the behaviour  of matter and interaction with energy on the scale of atoms and atomic particles i.e., particles of the size of the order of   1/10¹⁰ metres.

Phenomena such as motion of mechanical objects involving distances larger than about  1/10⁶ metres can be explained satisfactorily by laws of classical theoretical physics which is based on the following basic laws : 

1) Newton's Laws of motion, 

2) Newton's inverse square law of gravitational attraction between two bodies, 

3) Coulomb's inverse square law of attraction or repulsion between two electrically charged bodies, 

4) The law of force on a moving charge in a magnetic field, i.e., the Lorentz force.

However, certain phenomena such as spectral distribution of energy in blackbody radiation, Photoelectric effect etc; and phenomena involving distances of the order of 1/10¹⁰ metres could not be explained by classical mechanics. 

These limitations or failure of classical mechanics led to the development of quantum mechanics, the major revolution in Physics. The above limitation i.e., the energy distribution in the spectrum of a black body was successfully explained by Max planck in 1900 who proposed the revolutionary concept of quantum hypothesis. This was origin of the Quantum theory.

FAILURE OF CLASSICAL MECHANICS 

There are many important experimental results which could not be explained on the basis of classical mechanics. Some of them are:

1) Stability of atoms and molecules. According to classical mechanics, the atom is stable. When electron revolves around the nucleus in a circular orbit, it has acceleration. We know that any accelerating charge emits the radiation.

The electron during its motion around the nucleus should have limited energy continuously and as a result the radius of revolution would have reduced continuously and ultimately the electron would have much into the nucleus. But this is against the stability of the atom.

 In other words, the classical theory could not explain the stability of the atoms and molecules. The classical theory, has no explanation to the behaviour in the region of atomic dimensions.

2) The atomic spectra. Characteristic frequency emission or absorption by the elements.

3) The regularities among the spectral lines.

4) The specific heat of solids at low temperatures.

5) The Black Body radiation. The quantity and quality of the emitted radiation depends only on the temperature of the body and not on the nature of the material of the body. Moreover, the radiation emitted at a particular temperature consists of wide range of frequencies with different intensities.

6) The photoelectric-effect(click here) . The photo-electric emission and scattering of free electrons.

7) The emission of X-Rays(click here for Details), radioactivity and other nuclear activities.

CONCLUSION

The faliure of classical mechanics (which includes Newton's laws of motion, inverse law of gravitational attraction between two bodies, coulomb's inverse law of attraction or repulsion between two charged bodies, law of Lorentz force etc.) led to the development of Quantum Mechanics. To overcome, this discrepancy,  German scientists Max Plank in 1900, proposed his new theory,  now known as old quantum theory. This theory was applied to many crucial problems of microscopic dimensions and got the satisfactory solution.

Many distinguished physicists Albet Einstein, Neils Bohr, Louis de Broglie, Max Born, Paul Dirac, Werner Heisenberg, Wolfgang Pauli Erwin Schrödinger, Richard Feynman, Compton contributed to the development of Quantum mechanics.

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