Suppose an electron and a proton move at the same speed. which particle has a longer de broglie wavelength? suppose an electron and a proton move at the same speed. which particle has a longer de broglie wavelength? the proton has the longer de broglie wavelength. since both are particles, it is meaningless to discuss a wavelength associated with them. both have the same de broglie wavelength. the electron has the longer de broglie wavelength.