# Question Video: Calculating Electron Flow due to a Constant Current

How many electrons flow through a point in a wire in 3.00 s if there is a constant current of 4.00 A?

02:05

### Video Transcript

How many electrons flow through a point in a wire in 3.00 of seconds, if there is a constant current of 4.00 amps?

We can call the time value given of 3.00 seconds π‘. And the current of 4.00 amps, weβll call πΌ. We want to know the number of electrons flowing through a point in a wire. Weβll call that number capital π. We can start by recalling the definition of electrical current. Current πΌ is equal to the amount of charge π flowing past a point in sometime π‘ in seconds.

In our case, both πΌ and π‘ are quantities given in the exercise statement. If we rearrange this equation to solve for π, seeing that itβs πΌ times π‘, we know itβs not exactly π we want to solve for but π the number of charged particles, particularly electrons, flowing through a point in the wire. The total charge π represented in this current is equal to the charge on an individual electron times the number of electrons in the current. In other words, π equals the charge on an electron times π which equals πΌ times π‘.

We can now rearrange this equation to solve for π. When we do, we see that π is πΌ times π‘ divided by the charge on an electron. If we assume positive charge carriers as is assumed in conventional current, then weβll take the magnitude of that charge of an electron in our equation. We can recall that the charge on a single electron is negative 1.6 times 10 to the negative 19th coulombs. Knowing that, we know all three values to plug in and solve for π.

When we do and enter these values on our calculator, we find that π is 7.50 times 10 to the 19th. This is the number of electrons passing through a point in the wire under these conditions.