Part of the Electronics glossary:

Also see current, voltage, resistance,and Ohm's Law.

Electrical power is the rate at which electrical energy is converted to another form, such as motion, heat, or an electromagnetic field. The common symbol for power is the uppercase letter P. The standard unit is the watt,symbolized by W. In utility circuits, the kilowatt (kW) is often specified instead;1 kW = 1000 W.

One watt is the power resulting from an energy dissipation, conversion, or storage process equivalent to one joule per second. When expressed in watts, power is sometimes called wattage. The wattage in a direct current (DC) circuit is equal to the product of the voltage in volts and the current in amperes. This rule also holds for low-frequency alternating current (AC) circuits in which energy is neither stored nor released. At high AC frequencies, in which energy is stored and released (as well as dissipated or converted), the expression for power is more complex.

In a DC circuit, a source of E volts, deliveringIamperes, produces P watts according to the formula:

P = EI

When a current of I amperes passes through a resistance of Rohms, then the power in watts dissipated or converted by that component is given by:

P = I2R

When a potential difference of E volts appears across a component having a resistance of R ohms, then the power in watts dissipated or converted by that component is given by:

P = E2/R

In a DC circuit, power is a scalar (one-dimensional) quantity. In the general AC case, the determination of power requires two dimensions, because AC power is a vector quantity. Assuming there is no reactance (opposition to AC but not to DC) in an AC circuit, the power can be calculated according to the above formulas for DC, using root-mean-square values for the alternating current and voltage. If reactance exists, some power is alternately stored and released by the system. This is called apparent power or reactive power. The resistance dissipates power as heat or converts it to some other tangible form; this is called true power. The vector combination of reactance and resistance is known as impedance.

This was last updated in January 2008
Contributor(s): Jerome Kelly
Posted by: Margaret Rouse

Related Terms

Definitions

  • flash storage

    - Flash storage, based on flash memory, is used for data repositories, storage systems and consumer devices, such as USB drives, smartphones and solid-state drives. Flash-based storage is faster than... (WhatIs.com)

  • digital assistant

    - A digital assistant is an application program that can understand natural human language and complete electronic tasks for the end user. (WhatIs.com)

  • media center PC

    - A media center PC is a dedicated computer connected to the user's digital TV. The computer components are typically chosen for characteristics such as low power consumption, low heat dissipation, i... (WhatIs.com)

Glossaries

  • Electronics

    - Terms related to electronics, including definitions about electrical components and words and phrases about computers, laptops parts, digital cameras, televisions and home appliances.

  • Internet applications

    - This WhatIs.com glossary contains terms related to Internet applications, including definitions about Software as a Service (SaaS) delivery models and words and phrases about web sites, e-commerce ...

Ask a Question. Find an Answer.Powered by ITKnowledgeExchange.com

Ask An IT Question

Get answers from your peers on your most technical challenges

Ask Question

Tech TalkComment

Share
Comments

    Results

    Contribute to the conversation

    All fields are required. Comments will appear at the bottom of the article.