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? [3 MARKS]

Answer 1

Each point: 1 Mark

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

Time, t = 1 s

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

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

So, no. of electrons striking per second = $\frac{(10\times {10}^{-6}C)}{(1.6\times {10}^{-19}C)}=6.25\times {10}^{13}$

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