Question

Point p, to me, doesn't look like a conjunction point where I can apply Kirchhoff's first law, which is the sum of the current in is equal to the sum of the current out. And how do I explain using charges that flow through?

Answer 1

ANSWER

a) The current at P is 1.0A and it is moving towards the node.

b) A total of 1C charges flow through P in 1.0 seconds

EXPLANATION

a) To find this, we have to apply Kirchoff's node law which states that:

Therefore, we have that:

$4.0+3.0-8.0+P=0$

Solve for P:

$\begin{gathered} 4.0+3.0-8.0+P=0 \\ -1.0+P=0 \\ \Rightarrow P=1.0A \end{gathered}$

This implies that the current at point P is 1A and it is moving towards the node (in the left direction).

b) To find the electric charge that flows through P in 1.0s, we have to use the formula for current:

$I=\frac{q}{t}$

where I = current, q = electric charge and t = time

Therefore, we have to find q:

$\begin{gathered} q=I\cdot t \\ \Rightarrow q=1.0\cdot1.0 \\ q=1.0C \end{gathered}$

Therefore, a total of 1C charges flow through P in 1.0 seconds.