Question

If Bohr’s quantisation postulate $\left(\right(\text{angular momentum}=\frac{nh}{2\pi })$ 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?

Answer 1

According to Bohr’s postulate, angular momentum $=\frac{nh}{2\pi }$

As the mass of any planet is very large, so its angular momentum will be very high and angular momentum is directly proportional to n, therefore, it has higher quantum number.

Now, according to Bohr energy is inversely proportional to the quantum number. So, the difference between energy states will becomes very small.

Hence, energy states are rather continuous or not quantized.

Therefore, quantization theory is not applicable to the planetary motion.

Final Answer: 𝑛 will be high and difference in energy levels will be low.