Browse Definitions :
Definition

reactance

Reactance, denoted X, is a form of opposition that electronic components exhibit to the passage of alternating current (alternating current) because of capacitance or inductance.  In some respects, reactance is like an AC counterpart of DC (direct current) resistance.  But the two phenomena are different in important ways, and they can vary independently of each other.  Resistance and reactance combine to form impedance, which is defined in terms of two-dimensional quantities known as complex number.

When alternating current passes through a component that contains reactance, energy is alternately stored in, and released from, a magnetic field or an electric field.  In the case of a magnetic field, the reactance is inductive.  In the case of an electric field, the reactance is capacitive.  Inductive reactance is assigned positive imaginary number values.  Capacitive reactance is assigned negative imaginary-number values.

As the inductance of a component increases, its inductive reactance becomes larger in imaginary terms, assuming the frequency is held constant.  As the frequency increases for a given value of inductance, the inductive reactance increases in imaginary terms.  If L is the inductance in henries (H) and f is the frequency in hertz (Hz), then the inductive reactance +jXL, in imaginary-number ohms, is given by:

+jXL = +j(6.2832fL)

where 6.2832 is approximately equal to 2 times pi, a constant representing the number of radians in a full AC cycle, and j represents the unit imaginary number (the positive square root of -1).  The formula also holds for inductance in microhenries (?H) and frequency in MHz (MHz).

As a real-world example of inductive reactance, consider a coil with an inductance of 10.000 ?H at a frequency of 2.0000 MHz.   Using the above formula, +jXL is found to be +j125.66 ohms.  If the frequency is doubled to 4.000 MHz, then +jXL is doubled, to +j251.33 ohms.  If the frequency is halved to 1.000 MHz, then +jXL is cut in half, to +j62.832 ohms.

As the capacitance of a component increases, its capacitive reactance becomes smaller negatively (closer to zero) in imaginary terms, assuming the frequency is held constant.  As the frequency increases for a given value of capacitance, the capacitive reactance becomes smaller negatively (closer to zero) in imaginary terms.  If C is the capacitance in farads (F) and f is the frequency in Hz, then the capacitive reactance -jXC, in imaginary-number ohms, is given by:

-jXC = -j (6.2832fC)-1

This formula also holds for capacitance in microfarads (?F) and frequency in megahertz (MHz).

As a real-world example of capacitive reactance, consider a capacitor with a value of 0.0010000 ?F at a frequency of 2.0000 MHz.  Using the above formula, -jXC is found to be -j79.577 ohms.  If the frequency is doubled to 4.0000 MHz, then -jXC is cut in half, to -j39.789 ohms.  If the frequency is cut in half to 1.0000 MHz, then -jXC is doubled, to -j159.15 ohms.

This was last updated in September 2005

• ISO 31000 Risk Management

The ISO 31000 Risk Management framework is an international standard that provides businesses with guidelines and principles for ...

• pure risk

Pure risk refers to risks that are beyond human control and result in a loss or no loss with no possibility of financial gain.

• risk reporting

Risk reporting is a method of identifying risks tied to or potentially impacting an organization's business processes.

In cryptography, a one-time pad is a system in which a randomly generated private key is used only once to encrypt a message that...

• What is cyber hygiene and why is it important?

Cyber hygiene, or cybersecurity hygiene, is a set of practices individuals and organizations perform regularly to maintain the ...

• Pretty Good Privacy (PGP)

Pretty Good Privacy or PGP was a popular program used to encrypt and decrypt email over the internet, as well as authenticate ...

• What is risk mitigation?

Risk mitigation is a strategy to prepare for and lessen the effects of threats faced by a business.

• fault-tolerant

Fault-tolerant technology is a capability of a computer system, electronic system or network to deliver uninterrupted service, ...

• synchronous replication

Synchronous replication is the process of copying data over a storage area network, local area network or wide area network so ...

• information lifecycle management (ILM)

Information lifecycle management (ILM) is a comprehensive approach to managing an organization's data and associated metadata, ...

• WORM (write once, read many)

In computer media, write once, read many, or WORM, is a data storage technology that allows data to be written to a storage ...

• direct access

In computer storage, direct access is the process of reading and writing data on a storage device by going directly to where the ...

Close