Question

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

• A. $10^{-19}$
• B. $10^{-17}$
• C. $10^{18}$
• D. $10^{17}$

Answer 1

Answer: (B)

We know that
current $(I)=$ charge $(q)\times$ time $(t)$ ...(i)
Also, time $(t)=\frac{1}{\text{ frequency }(n)}$ ...(ii)
From Eqs. (i) and (ii), we get
$n=\frac{q}{I}$
Given, $q=1.6\times 10^{-19}C$,
$I=16mA=16\times 10^{-3}A$
$n=\frac{1.6\times 10^{-19}}{16\times 10^{-3}}=10^{-17}$