Two electrons are moving with same speed v. One electron enters a region of uniform electric field while the other enters a region of uniform magnetic field, then after
some time de Broglie wavelengths of two are ${\lambda }_1$ and ${\lambda }_2$ respectively. Now,

Speed of electron which enters into electric field may increase or decrease depending on direction of electric field while for second electron, since magnetic force is perpendicular to direction of velocity, it remains constant.

$\text{ So, from }\lambda =\frac{h}{m{v}^{\mathrm{\prime }}}$

${\lambda }_1>{\lambda }_2\text{ or }{\lambda }_1<{\lambda }_2$