Question

A potential barrier of $0.4V$ exists across a $p-n$ junction. An electron enters the junction from the $n$-side with a speed of $6.0\times 10^{5}m{s}^{-1}$. The speed with which electron enters the $p$ side will be $\frac{x}{3}\times 10^{5}m{s}^{-1}$ the value of $x$ is ___. (Given mass of electron $=9\times 10^{-31}kg$, charge on electron $=1.6\times 10^{-19}C$.)

Answer 1

Answer: 14

Work done by Electric field $=K_f-K_i$
$\frac{1}{2}m{v}^2-\frac{1}{2}m{u}^2=-1.6-10^{-19}\times 0.4$
$\frac{1}{2}9\times 10^{-31}\left(v^2-u^2\right)=-0.64\times 10^{-19}$
$u^2-v^2=\frac{2\times 0.64\times 10^{12}}{9}$
$v^2=\left(36-\frac{128}{9}\right)\times 10^{10}$
$v=\frac{14}{3}\times 10^{5}m/s$
$x=14$