The wavelength λeof an electron and λpof a photon of same energy E are related by

Wavelength of an electron of energy E isλe=h2meE          −−−iWavelength of a photon of same energy E isλp=hcE    or   E=hcλp          −−−iiSquaring both sides of Eq. (i), we getλe2=h22meE   or  E=h22meλe2        −−−iiiEquating (ii) and (iii), we gethcλp=h22meλe2 λp=2mechλe2 λp∝λe2