The work function of $Cu$ is $7.68 \times 10^{-19} \ J$. If photons of wavelength $221 \ nm$ are made to strike the surface of the metal,the kinetic energy (in $J$) of the ejected electrons will be $\left(h=6.63 \times 10^{-34} \ Js, c=3 \times 10^8 \ ms^{-1}\right)$.

The energy of an electron revolving in the $n^{th}$ Bohr's orbit of an atom is given by the expression

In the transition of an electron in an atom,its kinetic energy changes from $y$ to $y/4$. The change in potential energy $(P.E.)$ will be:

$A$ 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 first quantum mechanical model of the atom was proposed by ........

The figure that is not a direct manifestation of the quantum nature of atoms is: