The conservation of energy and conservation of charge when applied to electrical circuits are known as Kirchoff's laws.

*Conservation of energy* - zero algebraic sum of the voltage drops
around a closed circuit loop (imaginary loop)

*Conservation of charge* - zero algebraic sum of the currents
flowing into a point (total charge in, equals total charge out)

When applying these laws to solve for circuit unknowns we will find the following definitions useful:

- an
*element*is an impedance (resistance) or EMF (ideal voltage source or ideal current source), - a
*node*is a point where three or more current-carrying elements are connected, - a
*branch*is one element or several in series connecting two adjacent nodes, and - an
*interior loop*is a circuit loop not subdivided by a branch.

Using these definitions we can apply Kirchoff's laws to a circuit to solve for the unknown quantities. The general procedure is:

- define the currents and voltages on a diagram,
- apply Kirchoff's laws to loops and nodes,
- write down a set of linear algebraic equations, and
- solve for the unknowns.

But before we look at general circuits lets consider how simple resistors add.

- Series and Parallel Combinations of Resistors
- Voltage Divider
- Current Divider
- Branch Current Method
- Loop Current Method

Tue Jul 13 16:55:15 EDT 1999