Kirchhoff's 1st Law
This is a branch. A branch is a path between two nodes which is able to absorb or deliver energy in an electric circuit.
This is a node. A node is a point where two or more branches of a circuit connect.
Test it out
Tap the diagram for more information and click on the buttons to change a component and see what happens!
 One Branch In Many Branches In Many Branches In & Out
Example calculations
In order to work with Kirchhoff's 1st Law, electrical engineers need to understand and work with a variety of calculations. Here are just a few:
One branch in:
$I_1 = I_2 + I_3$
$I_1 - I_2 - I_3 = 0$
Many branches in:
$I_1 + I_2 + I_3 = I_4$
$I_1 + I_2 + I_3 - I_4 = 0$
One branch in:
$I_1 + I_2 = I_3 + I_4$
$I_1 + I_2 - I_3 - I_4 = 0$
 Current $I$ Voltage $V$ Resistor $R$
Cars and manufacturing facilities have extensive electrical systems consisting of hundreds of circuits working to relay power. Kirchhoff’s 1st Law allows us to analyse and understand how electrical current flows along multiple paths and across multiple components.
Because of this law, we know that if several conductor branches meet at a point, or node, the total currents flowing towards the juncture point is equal to the total current leaving the same point. In other words, the sum of the values of currents in, and currents out, is equal to zero.
By applying these laws, we can easy solve complicated calculations, adjust current values to regulate the flow of electrical energy and ensure the components through which the electricity flows are adequately protected and provided for.
Practice Questions
Test your new knowledge on Kirchhoff's first law by answering these questions.
1. Kirchhoff’s 1st Law is also referred to as
2. The place where two or more circuits meet is called a
3. Currents I1 and I2 are flowing into the node and currents I3 and I4 are flowing out. Calculate the value of I3 if I1 = 100A, I2 = 50A and I4 = 75A
Formula:
$I_1 + I_2 + I_5 = I_3 + i_4$