The ground state energy of hydrogen atom is $$-13.6 ~\mathrm{eV}$$. The energy needed to ionize hydrogen atom from its second excited state will be :

The wavelength of Lyman series of hydrogen atom appears in:

The angular momentum of an electron moving in an orbit of hydrogen atom is $$\mathrm{1.5\left(\frac{h}{\pi}\right)}$$. The energy in the same orbit is nearly.

The half life of a radioactive substance is 20 minutes. In how much time, the activity of substance drops to $$\left(\frac{1}{16}\right)^{\text {th }}$$ of its initial value?