Question

A potential barrier of $0.4\, V$ exists across a $p-n$ junction. An electron enters the junction from the $n$-side with a speed of $6.0 \times 10^{5} ms ^{-1}$. The speed with which electron enters the $p$ side will be $\frac{x}{3} \times 10^{5} ms ^{-1}$ 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

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