What is ohm? - Definition from WhatIs.com
Part of the Smart grid glossary:

The ohm is the standard unit of electrical resistance in the International System of Units ( SI ). Ohms are also used, when multiplied by imaginary numbers, to denote reactance in alternating-current ( AC ) and radio-frequency ( RF ) applications. Reduced to base SI units, one ohm is the equivalent of one kilogram meter squared per second cubed per ampere squared (1 kg times m 2 · s -3 · A -2 . The ohm is also the equivalent of a volt per ampere (V/A).

In a direct-current ( DC ) circuit, a component has a resistance of one ohm when a potential difference of one volt produces a current of one ampere through the component. In AC and RF circuits, resistive ohms behave the same as they do in DC circuits, provided the root-mean-square ( rms ) AC voltage is specified. In AC and RF circuits, reactance exists only when there is a net capacitance or inductance . Capacitive reactances have negative imaginary ohmic values; inductive reactances have positive imaginary ohmic values. The reactance of a particular capacitor or inductor depends on the frequency.

Resistances and reactances are sometimes expressed in units representing power-of-10 multiples of one ohm. A kilohm is equal to one thousand (10 3 ) ohms. A megohm is equal to one million (10 6 ) ohms. Fractional prefix multiplier s are seldom used for resistance or reactances; rarely will you hear or read about a milliohm or a microhm. Extremely small resistances and reactances are usually referred to in terms of conductance.

Also see conductance , Ohm's Law , prefix multiplier s, resistance , reactance , siemens , and International System of Units ( SI ).

This was last updated in March 2010
Posted by: Margaret Rouse

Related Terms


  • smart grid

    - Smart grid is a generic label for the application of computer intelligence and networking abilities to a dumb electricity distribution system. (WhatIs.com)

  • sensor data

    - Sensor data is the output of a device that detects and responds to some type of input from the physical environment. The output may be used to provide information or input to another system or to g... (WhatIs.com)

  • sensor hub

    - A sensor hub is a connection point for multiple sensors that uses a multipoint control unit (MCU), coprocessor or digital signal processor (DSP) to compile and process data gathered from those sens... (WhatIs.com)


  • Smart grid

    - Terms related to smart grids, including definitions about utility electricity delivery systems and words and phrases about smart meters and distributing, monitoring and billing electrical power.

  • 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



    Contribute to the conversation

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