The wavelength of electrons accelerated from rest through a potential difference of 40 kV is $x \times 10^{-12} \mathrm{~m}$. The value of $x$ is $\_\_\_\_$ . (Nearest integer) Given : Mass of electron $=9.1 \times 10^{-31} \mathrm{~kg}$ Charge on an electron $=1.6 \times 10^{-19} \mathrm{C}$ Planck's constant $=6.63 \times 10^{-34} \mathrm{Js}$