Two series of spectral lines of atomic hydrogen which do not belong to the infrared spectral region are

As an electron moves away from the nucleus,its potential energy

Explain the photoelectric effect.

The ratio of the velocity of an electron in the ground state of a hydrogen atom to its velocity in the second excited state of a $He^{+}$ ion is:

When the electron of a hydrogen atom returns to the $L$ shell $(n=2)$ from shells of higher energy,we get a series of lines in the spectrum. This series is called:

If the binding energy of electrons in a metal is $250 \ kJ \ mol^{-1}$,what should be the threshold frequency of the striking photons in order to free an electron from the metal surface?