Browse Definitions:
Definition

# resistance

Resistance is the opposition that a substance offers to the flow of electric current.  It is represented by the uppercase letter R.  The standard unit of resistance is the ohm, sometimes written out as a word, and sometimes symbolized by the uppercase Greek letter omega:

When an electric current of one ampere passes through a component across which a potential difference (voltage) of one volt exists, then the resistance of that component is one ohm. (For more discussion of the relationship among current, resistance and voltage, see Ohm's law.)

In general, when the applied voltage is held constant, the current in a direct-current (DC) electrical circuit is inversely proportional to the resistance.  If the resistance is doubled, the current is cut in half; if the resistance is halved, the current is doubled.  This rule also holds true for most low-frequency alternating-current (AC) systems, such as household utility circuits. In some AC circuits, especially at high frequencies, the situation is more complex because some components in these systems can store and release energy, as well as dissipating or converting it.

The electrical resistance per unit length, area, or volume of a substance is known as resistivity. Resistivity figures are often specified for copper and aluminum wire, in ohms per kilometer.

Opposition to AC, but not to DC, is a property known as reactance.  In an AC circuit, the resistance and reactance combine vectorially to yield impedance.

Resistance contrasts with conductance, which is a measure of the ease with which electrical current flows through a substance.

See an introduction to electrical resistance:

This was last updated in July 2015

#### Join the conversation

Send me notifications when other members comment.
helped me to know about the topic
Cancel
good
Cancel
A for effort
Cancel
10/10
Cancel
penis
Cancel
its very useful
Cancel
Cancel

## SearchCompliance

• ### risk map (risk heat map)

A risk map, also known as a risk heat map, is a data visualization tool for communicating specific risks an organization faces.

• ### internal audit (IA)

An internal audit (IA) is an organizational initiative to monitor and analyze its own business operations in order to determine ...

• ### pure risk (absolute risk)

Pure risk, also called absolute risk, is a category of threat that is beyond human control and has only one possible outcome if ...

## SearchSecurity

• ### FIDO (Fast Identity Online)

FIDO (Fast ID Online) is a set of technology-agnostic security specifications for strong authentication. FIDO is developed by the...

• ### cryptanalysis

Cryptanalysis is the study of ciphertext, ciphers and cryptosystems with the aim of understanding how they work and finding and ...

• ### Trojan horse (computing)

In computing, a Trojan horse is a program that appears harmless, but is, in fact, malicious.

## SearchHealthIT

• ### HITECH (Health Information Technology for Economic and Clinical Health) Act of 2009

The HITECH (Health Information Technology for Economic and Clinical Health) Act of 2009 is legislation that was created to ...

• ### Epic Systems

Epic Systems is one of the largest providers of health information technology, used primarily by large U.S. hospitals and health ...

• ### accountable care organization (ACO)

An accountable care organization (ACO) is an association of hospitals, healthcare providers and insurers in which all parties ...

## SearchDisasterRecovery

• ### business continuity and disaster recovery (BCDR)

Business continuity and disaster recovery (BCDR) are closely related practices that describe an organization's preparation for ...

• ### business continuity plan (BCP)

A business continuity plan (BCP) is a document that consists of the critical information an organization needs to continue ...

• ### call tree

A call tree -- sometimes referred to as a phone tree -- is a telecommunications chain for notifying specific individuals of an ...

## SearchStorage

• ### SSD TRIM

SSD TRIM is an Advanced Technology Attachment (ATA) command that enables an operating system to inform a NAND flash solid-state ...

• ### cloud storage service

A cloud storage service is a business that maintains and manages its customers' data and makes that data accessible over a ...

• ### cloud hosting

Cloud hosting is the process of outsourcing an organization's computing and storage resources to a service provider that offers ...

## SearchSolidStateStorage

• ### hybrid hard disk drive (HDD)

A hybrid hard disk drive is an electromechanical spinning hard disk that contains some amount of NAND Flash memory.

Close