The frequency corresponding to the transition $n = 2$ to $n = 1$ in a hydrogen atom is:

If the speed of an electron in the Bohr's first orbit of a hydrogen atom is $x$,the speed of the electron in the third Bohr's orbit is:

Which one of the following statements is not correct?

When electromagnetic radiation of wavelength $310 \ nm$ falls on the surface of a metal having work function $3.55 \ eV$, the velocity of photoelectrons emitted is $x \times 10^5 \ ms^{-1}$. The value of $x$ is (Nearest integer). Given: $m_{e} = 9 \times 10^{-31} \ kg$, $h = 6.63 \times 10^{-34} \ J \cdot s$, $c = 3 \times 10^8 \ m/s$, $1 \ eV = 1.6 \times 10^{-19} \ J$.

Which of the following is $NOT$ observed in Rutherford's alpha-particle scattering experiment?

The ratio of kinetic energies of photoelectrons emitted from a metal by light of frequencies $v_1$ and $v_2$ is $1 : 2$. The threshold frequency of the metal will be: