The wavelength of electrons accelerated from rest through a...

De-broglie-wave length of electron:

{\lambda}_{e} = \dfrac{h}{\sqrt{2m ( KE )}}\left\{$\begin{array}{ll}∵ {e}^{-}\text{is accelerated} \\ \text{from rest} \\ ⇒ KE = q \times V\end{array}$\right)</p><p>\lambda = \dfrac{h}{\sqrt{2mqv}}$</p><p>$= \dfrac{6 . 63 \times {10}^{- 34}}{\sqrt{2 \times 1 . 6 \times {10}^{- 19} \times 9 . 1 \times {10}^{- 31} \times 40 \times {10}^{3}}}$</p><p>$= 0 . 614 \times {10}^{- 11}m$</p><p>$= 6 . 14 \times {10}^{- 12}m$</p><p>Nearest integer$= 6$</p><p>OR</p><p>$\lambda = \dfrac{12 . 3}{\sqrt{V}}Å$</p><p>$= \dfrac{12 . 3}{200} = 6 . 15 \times {10}^{- 12}m$</p><p>Ans. is$6