Question

A TV set picture tube shoots out a beam of electrons. The current due to this beam is 10mA. Then, the total number of electrons that will strike the TV screen every second are___

• A. $6.25\times {10}^{16}$
• B. $6.25\times {10}^{-16}$
• C. $3.125\times {10}^{16}$
• D. $5\times {10}^{16}$

Answer 1

The correct option is A

$6.25\times {10}^{16}$

Given, I = 10mA = $10\times {10}^{-3}A$

t = 1s.

The charge on one electron (e) = $1.6\times {10}^{-19}C$

Now, $I=\frac{q}{t}$
and, $q=n\times e$ (n is the number of electrons)
Hence, $I=\frac{n\times e}{t}$

Or, $n=\frac{I\times t}{e}$

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

=$6.25\times {10}^{16}$