The velocity of an electron in the $3^{rd}$ excited state of $Be^{3+}$ 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 $\left(h=6.63 \times 10^{-34} \ Js, c=3 \times 10^8 \ ms^{-1}\right)$.

Supposing the electron is present in the $4^{th}$ energy level of $H$ atom. When the electron returns to the ground state,the possible transitions would be:

In Rutherford's experiment,generally the thin foil of heavy atoms,like gold,platinum etc. have been used to be bombarded by the $\alpha$-particles. If the thin foil of light atoms like Aluminium etc. is used,what difference would be observed from the above results?

Which of the following transitions will emit the shortest wavelength?

The wavelength of the first line of the Balmer series is $656 \ nm$. Calculate the wavelength of the second line of this series. (Note: First line means $n=3 \to n=2$ and second line means $n=4 \to n=2$)