When the electron in hydrogen atom jumps from fourth Bohr orbit to second Bohr orbit, one gets the

In Balmer series, wavelength of first line is ' $\lambda_1$ ' and in Brackett series wavelength of first line is ' $\lambda_2$ ' then $\frac{\lambda_1}{\lambda_2}$ is

Bohr model is applied to a particle of mass ' $m$ ' and charge ' $q$ ' is moving in a plane under the influence of a transverse magnetic field ' $B$ '. The energy of the charged particle in the $n$th level will be ( $h=$ Planck's constant)

The angle made by orbital angular momentum of electron with the direction of the orbital magnetic moment is