In Bohr's model,if the atomic radius of the first orbit is ${r_0}$,then the radius of the fourth orbit is

The angular momentum of the electron in the third Bohr orbit of hydrogen atom is $l$. Its angular momentum in the fourth Bohr orbit is

In a hydrogen atom,let $R$,$v$,and $E$ denote the radius,velocity,and total energy of the electron,respectively. Then,the principal quantum number $n$ is proportional to which of the following?

The ratio of the speed of the electrons in the ground state of hydrogen to the speed of light in vacuum is

In Bohr's model of the hydrogen atom,let $PE$ represent potential energy and $TE$ represent total energy. When an electron transitions to a higher energy level,

The energy of a hydrogen atom in the ground state is $-13.6 \, eV$. The energy of the $He^+$ ion in the first excited state will be .... $eV$.