The energy of an electron in the $3^{rd}$ orbit of $H$-atom (in $J$) is approximately:

What is the ratio of the velocity of an electron in the ground state of a hydrogen atom to the velocity of an electron in the second excited state of $He^{+}$?

When $\alpha$-particles are sent through a thin metal foil,most of them go straight through the foil because (one or more are correct)

$A$ certain atomic transition from an excited state to the ground state of the hydrogen atom in one or more steps gives rise to four lines in the ultraviolet region of the spectrum. How many lines does this transition produce in the infrared region of the spectrum?

$A$ bulb of $40 \ W$ is producing light of wavelength $620 \ nm$ with $80 \%$ efficiency. The number of photons emitted by the bulb in $20 \ s$ is $(1 \ eV = 1.6 \times 10^{-19} \ J, hc = 12400 \ eV \ \mathring{A})$

Describe Rutherford's atomic model.