An electron initially present in an excited state of $H$ atom is further excited to another energy level by an incident photon. It releases $10$ photons while coming back to the ground state,out of which $7$ have higher energy than the incident photon. The electron was initially present in:

$A$ source of monochromatic radiation of wavelength $400 \, nm$ provides $1000 \, J$ of energy in $10 \, seconds$. When this radiation falls on the surface of sodium,$x \times 10^{20}$ electrons are ejected per second. Assume that wavelength $400 \, nm$ is sufficient for ejection of electrons from the surface of sodium metal. The value of $x$ is $......$. (Nearest integer) $(h = 6.626 \times 10^{-34} \, Js)$

When a hydrogen sample in the ground state is bombarded with electrons,what potential is required to accelerate the electrons so that the first Brackett line is emitted? $(eV)$

What is the angular momentum of an electron in the fourth orbit of a hydrogen atom?

The energy of an electron in a Hydrogen atom is given by the expression:

If the energy of the first orbit of $He^{+}$ is $-54.4 \, eV$,then the energy of the second orbit will be ............. $eV$.