Glossary
Algebraic Sum (of currents)
The sum of all currents at a junction, taking into account their assigned positive or negative signs based on whether they are entering or leaving. According to Kirchhoff's Junction Rule, this sum must equal zero.
Example:
If 5A enters a junction and 2A leaves, the algebraic sum would be +5A - 2A - I_unknown = 0, allowing you to solve for the unknown current.
Conservation of Electric Charge
A fundamental law stating that electric charge cannot be created or destroyed, only transferred from one location or object to another.
Example:
In a lightning strike, charge is transferred from the cloud to the ground, demonstrating the conservation of electric charge as no new charge is created.
Current
The rate of flow of electric charge through a conductor, typically measured in Amperes (A).
Example:
If a toaster draws 10 Amperes of current, it means 10 coulombs of charge pass through a point in its circuit every second.
Junction
A point in an electrical circuit where two or more circuit elements or wires connect, allowing current to split or combine.
Example:
In a household wiring system, a light switch acts as a junction where the circuit can be opened or closed, controlling the flow of electricity to the bulb.
Kirchhoff's Junction Rule
A fundamental principle in circuit analysis stating that the total current entering a circuit junction must equal the total current leaving it. It is a direct consequence of the conservation of electric charge.
Example:
When analyzing a parallel circuit, applying Kirchhoff's Junction Rule at the point where the main current splits helps determine how much current flows through each branch.
Sign Conventions (for current)
A set of rules used to assign positive or negative values to currents in circuit analysis, typically defining currents entering a junction as positive and those leaving as negative.
Example:
When solving a circuit problem, if you assume a sign convention where current flowing clockwise is positive, then a counter-clockwise current would be negative.