Two light waves amplitudes in the ratio $3:1$ produce interference. The ratio of the maximum to minimum intensity is

Photoelectric emission is observed from a metallic surface for frequencies $v_1$ and $v_2$ of the incident light rays ($v_1 > v_2$). If the maximum values of kinetic energy of the photoelectrons emitted in the two cases are in the ratio of $k : 1$, then what is the threshold frequency of the metallic surface?

A photon and an electron have equal energy E. The ratio of $\lambda$(electron) to $\lambda$(photon) is proportional to

The kinetic energy of the electron in an orbit of radius $r$ in hydrogen atom is proportional to ($e$ = electronic charge)