The ionization potential for the second $He$ electron is ...... $eV$.

In an atom,two electrons move around the nucleus in circular orbits of radii $R$ and $4R$. The ratio of the time taken by them to complete one revolution is:

Write the quantum condition suggested by Bohr for the angular momentum of the electron.

$A$ moving Hydrogen atom makes a head-on collision with a stationary Hydrogen atom. Before the collision,both atoms are in the ground state,and after the collision,they move together. The minimum kinetic energy of the moving Hydrogen atom,such that one of the atoms reaches the excitation state,is (in $eV$)

What is the angular momentum of an electron in Bohr's hydrogen atom whose energy is $-0.544 \ eV$?

What is the ratio of the equivalent electric currents produced by the motion of an electron in the first and second orbits of a hydrogen atom?