Question

The charge of an electron is $1.6\times {10}^{-19}\text{C}$. How many electrons strike the screen of a cathode ray tube each $\text{second}$ when the beam current is $16\text{mA}$?

• A. ${10}^{17}$
• B. ${10}^{19}$
• C. ${10}^{-19}$
• D. ${10}^{-17}$

Answer 1

The correct option is A ${10}^{17}$

Given:
$q=1.6\times {10}^{-19}\text{C};I=16\text{mA};t=1\text{s}$

As we know that

Current, $I=\frac{q}{t}=\frac{ne}{t}$

Where, $n=$ total numbers of electrons

$\Rightarrow 16\times {10}^{-3}=\frac{n\times 1.6\times {10}^{-19}}{1}$

$\therefore n={10}^{17}$

Hence, option $\left(a\right)$ is correct.

Key takeaway- electric current through an area is the rate of transfer of charge from one side of the area to the other.