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 × 105 ms–1. The speed with which electrons enters the p side will be
$\frac{x}{3} × 10^5$ ms-1
the value of x is _________.
(Give mass of electron = 9 × 10–31 kg, charge on electron = 1.6 × 10–19 C)

Answer 1

The correct answer is 14
Conserving energy,
$\frac{1}{2} mv² = \frac{1}{2} m ( 6 × 10^5)^2 - 0.4eV$
$⇒ v = \sqrt{( 6 × 10^5)^2 - \frac{2 × 1.6 × 10^{-19} × 0.4}{9 × 10^{-31} }}$
$=\sqrt{36 × 10^{10} - \frac{1.28}{9} × 10^{12}}$
$⇒ v = \frac{14}{3} × 10^5 m/s$
⇒ x = 14
There , the speed will be 14 m/s