The splitting of spectral lines under the influence of a magnetic field is known as .....

Which formula represents the rest mass of an electron?

Two radiations having energies $E_1$ and $E_2$ as $15 \ eV$ and $45 \ eV$ respectively,then the relationship between $\lambda_1$ and $\lambda_2$ will be:

The number of the following statements which is/are incorrect is:
$A$. Line emission spectra are used to study the electronic structure.
$B$. The emission spectra of atoms in the gas phase show a continuous spread of wavelength from red to violet.
$C$. An absorption spectrum is like the photographic negative of an emission spectrum.
$D$. The element helium was discovered in the sun by spectroscopic method.

Which of the following does not characterise $X$-rays?

$A$ photon of wavelength $6630 \mathring{A}$ is incident on a totally reflecting surface. The momentum delivered by the photon is equal to