Question

A TV set shoots out a beam of electrons. The beam current is $10\mu$A. How many electrons strike the TV screen in each second? How much charge strikes the screen in a minute?

Answer 1

1.
Beam current, $I=10\mu A=10\times {10}^{-6}A$
Time, $t=1s$

Hence, charge flowing per second:
$Q=It$
$Q=10\times {10}^{-6}\times 1$
$Q={10}^{-5}$ C

2.
We know that, charge on each electron is: $e=-1.6\times {10}^{-19}$ C

So, number of electrons striking per second,
$n=\frac{Q}{e}$
$n=\frac{{10}^{-5}C}{1.6\times {10}^{-19}C}$
$n=6.25\times {10}^{13}$

3. Now, charge striking the screen per minute,
$Q=I{t}^{\prime }$
$Q={10}^{-5}\times 60$
$Q=6\times {10}^{-4}C$