The difference in radii between the fourth and third Bohr orbits of $He^{+}$ (in $m$) is:

$A$ 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) $(h = 6.626 \times 10^{-34} \, Js)$

The angular momentum of an electron in the $7^{th}$ Bohr orbit of a hydrogen atom is given by:

When an electron in a hydrogen spectrum transitions from the $7^{th}$ energy level to the $1^{st}$ energy level,what is the total number of spectral lines produced?

If the ratio of energies of an electron in the excited states of $H$ and $Li^{2+}$ is $1: 9$,the radius ratio of the electron in the same excited states of $H$ and $Li^{2+}$ is

If the work function for the photoelectron emission of a metal is $3.75 \ eV$,then the threshold wavelength of the radiation needed for the ejection of the electron is approximately (in $nm$)