Three wires meet at a junction. Wire 1 has a current of 0.40 A into the junction. The current of wire 2 is 0.75 A out of the junction. How many electrons per second move past a point in wire 3?

number of electrons = 2.18*10^18 e

Explanation:

In order to calculate the number of electrons that move trough the second wire, you take into account one of the Kirchoff's laws. All the current that goes inside the junction, has to go out the junction.

Then, if you assume that the current of the wire 1 and 3 go inside the junction, then, all this current have to go out trough the second junction:

                (1)

i1 = 0.40 A

i2 = 0.75 A

you solve the equation i3 from the equation (1):

Next, you take into account that 1A = 1C/s = 6.24*10^18

Then, you have:

The number of electrons that trough the wire 3 is 2.18*10^18 e/s