Question

A potential barrier of $0.5\text{V}$ exists across a P-N junction. An electron approaches the junction from inside, with a speed of $5\times {10}^5\text{m/s}$. With what speed will it enter the P-side?

• A. $2.7\times {10}^5\text{m/s}$
• B. $1.7\times {10}^5\text{m/s}$
• C. $1\times {10}^5\text{m/s}$
• D. $3.5\times {10}^5\text{m/s}$

Answer 1

The correct option is A $2.7\times {10}^5\text{m/s}$


According to concentration of energy principle,

$\frac{1}{2}m{V}_1^2=eV+\frac{1}{2}m{V}_2^2$

$\Rightarrow \frac{1}{2}\times 9.1\times {10}^{-31}\times (5\times {10}^5{)}^2$
$=1.6\times {10}^{-19}\times 0.5+\frac{1}{2}\times (9.1\times {10}^{-31})V_2^2$

$\Rightarrow 1.13\times {10}^{-19}=0.8\times {10}^{-19}+4.55\times {10}^{-31}{V}_2^2$

$\Rightarrow v_2\approx 2.7\times {10}^5\text{m/s}$

Hence, $\left(A\right)$ is the correct answer.