A beam of electron is used in Young's double slits experiment. The slit width is d. When velocity of electron is increased, then : 

Fringe width decreases

$ \lambda = \frac{h}{mv}$

$\text{ As velocity is increased wavelength will decrease.}$

$\text{Fringe Width }\beta = \frac{\lambda D}{d}$

$\text{As wavelength decreases fringe width will also decrease.}$