Hydrogen atom is excited from ground state to another state with principal quantum number equal to $4$. Then the number of spectral lines in the emission spectra will be

In an atom, two electrons move around the nucleus in circular orbits of radii $R$ and $4R.$ The ratio of the time taken by them to complete one revolution is : (neglect electric interaction)

In gold foil experiment number of deflected $\alpha -$ particles at angle $90^o$ is $63$ than number of $\alpha -$ particle deflected at $120^o$ is

What radioactive source did the Geiger and Marsden use in the scattering experiment?

In the Rutherford's nuclear model of the atom, the nucleus (radius about $10^{-15} \;m$ ) is analogous to the sun about which the electron move in orbit (radius $\approx 10^{-10} \;m$ ) like the earth orbits around the sun. If the dimensions of the solar system had the same proportions as those of the atom, would the earth be closer to or farther away from the sun than actually it is? The radius of earth's orbit is about $1.5 \times 10^{11} \;m.$ The radius of sun is taken as $7 \times 10^{8}\;m$

Ratio of longest wave lengths corresponding to Lyman and Balmer series in hydrogen  spectrum is