The energy of an electron in a Hydrogen atom is given by the expression:

The work function of a metal is $4.2 \, eV$. If radiation of $2000 \, \mathring{A}$ falls on the metal,then the kinetic energy of the fastest photoelectron is:

What is the ratio of time periods $(T_1 / T_2)$ in the second orbit of a hydrogen atom to the third orbit of a $He^{+}$ ion?

The radii of the first,second,third,and fourth Bohr orbits of hydrogen are respectively:

The ionization energy of a $H$ atom is $13.6 \, eV$. The energy required to excite the electron from the ground state $(n=1)$ to the first excited state $(n=2)$ is ... $eV$.

If the radius of an electron in the excited state of $He^{+}$ is $0.4232 \ nm$, the energy of the electron in that excited state in $J$ is: (The radius and energy of an electron in the first orbit of a hydrogen atom are $52.9 \ pm$ and $-2.18 \times 10^{-18} \ J$ respectively)