# DC Circuit Equations and Laws

### Ohm's and Joule's Laws

#### Ohm's Law

#### Joule's Law

*Where*,

E = Voltage in volts

I = Current in amperes (amps)

R = Resistance in omhs

P = Power in watts

NOTE: the symbol "V" ("U" in Europe) is sometimes used to represent voltage instead of "E". In some cases, an author or circuit designer may choose to exclusively use "V" for voltage, never using the symbol "E." Other times the two symbols are used interchangeably, or "E" is used to represent voltage from a power source while "V" is used to represent voltage across a load (voltage "drop").

### Kirchhoff's Laws

*"The algebraic sum of all voltages in a loop must equal zero."*

**Kirchhoff's Voltage Law (KVL)**

*"The algebraic sum of all currents entering and exiting a node must equal zero."*

**Kirchhoff's Current Law (KCL)**

**Lessons In Electric Circuits** copyright (C) 2000-2020 Tony R. Kuphaldt, under the terms and conditions of the *CC BY License**.*

**Lessons In Electric Circuits**

*CC BY License*

*.*

See the Design Science License (Appendix 3) for details regarding copying and distribution.

Revised July 25, 2007

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