Question

The potential difference applied to an X-ray tube is 5 kV and the current flowing through it is 3.2 mA. Then what is the number of electrons striking the target per second? [The charge of one electron is $e=-1.6\times {10}^{-19}C$]

• A. $2\times {10}^{16}$
• B. $5\times {10}^{16}$
• C. $1\times {10}^{16}$
• D. $4\times {10}^{16}$

Answer 1

The correct option is A $2\times {10}^{16}$

Let $n$ be the number of electrons hitting the target and $t$ be the total time during which X-ray tube was in working condition.

We know that, total charge = number of electrons $\times$ charge of one electron.

So, $Q=n\times e$ ... (1)

Also, $Q=I\times t$ ... (2) where $I$ is the current and $t$ is the time.

From (1) and (2)

$n\times e=I\times t$

Therefore, $\frac{n}{t}=\frac{I}{e}=\frac{3.2\times {10}^{-3}}{-1.6\times {10}^{-19}}$

$\Rightarrow$ Number of electrons striking the target per second $=2\times {10}^{16}$ [Ignoring the negative charge of an electron and only considering the magnitude to find the number of electrons]