Electrons are accelerated through a potential difference V and protons are accelerated through a potential difference 4 V. The de-Broglie wavelengths are ${\text{λ}}_{\mathrm{e}} \mathrm{and} {\mathrm{\lambda }}_{\mathrm{p}}$ for electrons and protons respectively. The ratio of $\frac{{\mathrm{\lambda }}_{\mathrm{e}}}{{\mathrm{\lambda }}_{\mathrm{p}}}$ is given by  (given m_e is mass of electron and m_p is mass of proton).