Answer:
a. 1.56 × 10¹⁸ electrons per second
b. The electrons in wire 3 flow into the junction.
Explanation:
Here is the complete question
Three wires meet at a junction. Wire 1 has a current of 0.40 A into the junction. The current of wire 2 is 0.65 A out of the junction. (a) How many electrons per second move past a point in wire 3? (b) In which direction do the electrons move in wire 3 -- into or out of the junction?
Solution
(a) How many electrons per second move past a point in wire 3?
Using Kirchhoff's current law, at the junction, i₁ + i₂ + i₃ = 0 where i₁ = current in wire 1 = 0.40 A, i₂ = current in wire 2 = 0.65 A and i₃ = = current in wire 3,
So, i₃ = -(i₁ + i₂)
taking current flowing into the junction as positive and those leaving as negative, i₁ = + 0.40 A and i₂ = -0.65 A
So, i₃ = -(i₁ + i₂)
i₃ = -(0.40 A + (-0.65 A))
i₃ = -(0.40 A - 0.65 A)
i₃ = -(-0.25 A)
i₃ = 0.25 A
Since i₃ = 0.25 C/s and we have e = 1.602 × 10⁻¹⁹ C per electron, then the number of electrons flowing in wire 3 per second is i₃/e = 0.25 C/s ÷ 1.602 × 10⁻¹⁹ C per electron = 0.1561 × 10¹⁹ electrons per second = 1.561 × 10¹⁸ electrons per second ≅ 1.56 × 10¹⁸ electrons per second
(b) In which direction do the electrons move -- into or out of the junction?
Given that i₃ = + 0.25 A and that positive flows into the junction, thus, the electrons in wire 3 flow into the junction.
