An electron in an atom jumps in such a way that its kinetic energy changes from $x$ to $\frac{x}{4}$. The change in potential energy will be

The ratio of velocity of electron in the second orbit of $He^{+}$ to the third orbit of $B^{4+}$ is $:-$

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 $\left(h=6.63 \times 10^{-34} \ Js, c=3 \times 10^8 \ ms^{-1}\right)$.

When $\alpha$-particles are sent through a thin metal foil,most of them go straight through the foil because

What will be the number of photons required to obtain $1 \ J$ of energy by radiation having a wavelength of $4000 \ \mathring{A}$?

Observe the following statements:
Statement-$I$: Rutherford model of an atom cannot explain the stability of an atom.
Statement-$II$: The wavelength of $X$-rays is higher than the wavelength of microwaves.
The correct answer is: