Question

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

Answer 1

The charge of an electron is 1.6 x 10-19C.

Thus for a current of 10 mA, the charge going to screen in one scond is 10 mC

thus number of electrons, n = (10 x 10-3)/(1.6 x 10-19) = 6.25 x 1016

In a minute charge striking the screen = 10 * 60 = 600 mC

Answer 2

"The number of electrons striking the screen per second is $6.25 \times 10^{13}.$

The charge of the beam striking the screen per minute is 0.6 mC.

Given

Current, $\mathrm{I}=10 \mu \mathrm{A}$

Charge of an electron, $e=1.6 \times 10^{-19} \mathrm{C}$

Number of electrons striking the screen per second, n =?

Charge striking the screen per minute, q = ?

Solution:

We know that the charge of the beam can be found using,

q=It

When time t = 1 s,

$q=I \rightarrow(1)$

We know that the charge of an electron beam is given by

q=n e

Substituting equation (1) in the above equation, we get

ne = I

$\Rightarrow n=\frac{I}{e}$

Substitution

$n=\frac{10 \times 10^{-6}}{1.6 \times 10^{-19}}=6.25 \times 10^{13}$

When t=60s,

$q=10 \times 10^{-6} \times 60=6 \times 10^{-4} C$

$q=0.6 \mathrm{mC}$"