Kirchoff's First Law - The Current Law, (KCL)
"The total current or charge entering a junction or node is exactly equal to
the charge leaving the node as it has no other place to go except to leave, as no charge is
lost within the node".
In other words the algebraic sum of ALL the currents entering and leaving a node
must be equal to zero,
I(exiting) + I(entering) = 0.
This idea by Kirchoff is known as the Conservation of Charge.
Here, the 3 currents entering the node, I1, I2, I3 are all positive in value and the 2
currents leaving the node, I4 and I5 are negative in value.
Then this means we can also rewrite the equation as;
I1 + I2 + I3 - I4 - I5 = 0