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If Bohr’s quantisation postulate (angular momentum = nh/2p) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why then do we never speak of quantisation of orbits of planets around the sun?

If Bohr’s quantisation postulate (angular momentum = nh/2p) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why then do we never speak of quantisation of orbits of planets around the sun?

Grade:11

2 Answers

Saurabh Koranglekar
askIITians Faculty 10335 Points
3 years ago

The quantization of the orbits of the planetary motions is not considered in the same manner as the Bohr's quantization postulates for the atoms because the value of the angular momentum in terms of the Plank's constanthwill be of the order of1070h. The high value of the angular momentum leads to the quantum levels of the order of1070.
The energy and the angular momentum for such high values of n will be comparatively very small which is not possible in case of the planets.
Saurabh Koranglekar
askIITians Faculty 10335 Points
3 years ago
We never speak of quantization of orbits of plantes around the Sun because the angular momentum associated with planetary motion is largely relative to the value of Planck's constant (h). The angular momentum of the Earth in its orbit is of the order of1070h1070h. This leads to a very high value of quantum levels n of the order of10701070. For large values of n, successive energies and angular momenta are relatively very small. Hence, the quantum levels for planetary motion are considered continuous.

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