An electron in a hydrogen atom is replaced by an identically charged particle,a muon,with a mass $207$ times that of an electron. What will be the radius of the $K$ shell?

$A$ hydrogen atom,a deuteron atom,a $He^+$ ion,and a $Li^{++}$ ion each contain a single electron orbiting their nucleus. The wavelengths of the electromagnetic radiation emitted during the transition of the electron from the $n = 2$ orbit to the $n = 1$ orbit are found to be $\lambda_1, \lambda_2, \lambda_3$,and $\lambda_4$ respectively. Then:

Obtain an expression for the frequency of radiation emitted when a hydrogen atom de-excites from level $n$ to level $(n-1)$. For large $n$,show that this frequency equals the classical frequency of revolution of the electron in the orbit.

Radius of the second Bohr orbit of a singly ionized helium atom is ......... $ \mathring A $

An electron moves in a Bohr orbit. The magnetic field at the centre is proportional to

The Rydberg constant $R$ for hydrogen is