If the 0.300-mA current through the calculator mentioned in the Example 20.1 example is carried by electrons, how many electrons per second pass through it? Strategy The current calculated in the previous example was defined for the flow of positive charge. For electrons, the magnitude is the same,

Question

If the 0.300-mA current through the calculator mentioned in the Example 20.1 example is carried by electrons, how many electrons per second pass through it?
Strategy
The current calculated in the previous example was defined for the flow of positive charge. For electrons, the magnitude is the same, but the sign is opposite, [latex]I_{ ext {electrons }}=-0.300 imes 10^{-3} C / s[/latex]. Since each electron [latex]\left(e^{-} ight)[/latex] has a charge of [latex]-1.60 imes 10^{-19} C[/latex], we can convert the current in coulombs per second to electrons per second.

Accepted Answer

Starting with the definition of current, we have

[latex]I_{ ext {electrons }}=\frac{\Delta Q_{ ext {electrons }}}{\Delta t}=\frac{-0.300 imes 10^{-3} C }{ s }[/latex]. (20.5)

We divide this by the charge per electron, so that

[latex]\frac{e^{-}}{ s }=\frac{-0.300 imes 10^{-3} C }{ s } imes \frac{1 e^{-}}{-1.60 imes 10^{-19} C }[/latex] (20.6)

[latex]=1.88 imes 10^{15} \frac{e^{-}}{ s }[/latex].

Discussion
There are so many charged particles moving, even in small currents, that individual charges are not noticed, just as individual water molecules are not noticed in water flow. Even more amazing is that they do not always keep moving forward like soldiers in a parade. Rather they are like a crowd of people with movement in different directions but a general trend to move forward. There are lots of collisions with atoms in the metal wire and, of course, with other electrons.

Question 20.2: If the 0.300-mA current through the calculator mentioned in ...

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