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:

The energy and radius of an electron present in the second orbit of $He^{+}$ are respectively:

The $\alpha$-particle scattering experiment of Rutherford concluded that

How many spectral lines are obtained when an electron in a hydrogen atom undergoes a transition from the $7^{th}$ Bohr orbit to the $2^{nd}$ orbit?

Which of the following equations represents the velocity $(v)$ of the ejected electrons when a metal is struck with light of frequency $\nu$ and the threshold frequency of the metal is $\nu_0$? ($m_e =$ mass of electron and $h$ is Planck's constant).

$A$ certain metal has a work function of $\Phi = 2 \ eV$. It is irradiated first with $1 \ W$ of $400 \ nm$ light and later with $1 \ W$ of $800 \ nm$ light. Among the following,the correct statement is
[Given: Planck constant $(h) = 6.626 \times 10^{-34} \ J \ s$;
Speed of light $(c) = 3 \times 10^8 \ m \ s^{-1}$ ]