Kirchoff's 1st Law

Key Stage 5

Meaning

Kirchoff's 1st Law states that the total current entering a junction is equal to the total current leaving the junction.

About Kirchhoff's First Law

• Also known as the current law or junction rule.
• Kirchoff's 1st Law is based on the conservation of charge.
• Kirchoff's 1st Law is essential for analyzing complex electrical circuits.
• In Kirchoff's 1st Law the algebraic sum of currents at a junction is equal to zero.
• Kirchoff's 1st Law helps in solving circuit problems by setting up equations based on current conservation.
• Kirchoff's 1st Law is used in network analysis techniques such as mesh analysis and nodal analysis.
• Kirchoff's 1st Law applies to both DC and AC circuits.

Formula

• \(\sum I_n=I_1 + I_2 + I_3 +...=0\)

• \(\sum I_{in}=\sum I_{out}\)

Where:

• \(\sum I_n\) represents the sum of all currents at junction,

• \(I_1 + I_2 + I_3 +...\) represents the individual currents in each wire attached to the junction,

• \(\sum I_{in}\) represents the sum of all currents going into a junction,

• \(\sum I_{out}\) represents the sum of all currents leaving a junction

Examples

• In a parallel circuit, the sum of currents through each branch equals the total current entering the junction.
• Used to determine unknown currents in electrical network problems.