The de-Broglie's wavelength of an electron in the $4^{th}$ orbit is . . . . . . . . $\pi a_0$. ($a_0 =$ Bohr's radius)

The De Broglie wavelength $\lambda$ of an electron in the $2^{nd}$ Bohr orbit is:

$A$ stream of electrons from a heated filament was passed between two charged plates kept at a potential difference $V$ esu. If $e$ and $m$ are the charge and mass of an electron, respectively, then the value of $h/\lambda$ (where $\lambda$ is the wavelength associated with the electron wave) is given by:

If the total energy of an electron in a hydrogen atom in an excited state is $-3.4 \ eV$,then the de-Broglie wavelength of the electron is

The atomic masses of $He$ and $Ne$ are $4$ and $20 \ amu$,respectively. The value of the de Broglie wavelength of $He$ gas at $-73^{\circ} C$ is $M$ times that of the de Broglie wavelength of $Ne$ at $727^{\circ} C$. $M$ is

The velocity of a de Broglie wave is represented by which of the following expressions?