Browse Definitions:

wave number

The term wave number refers to the number of complete wave cycles of an electromagnetic field (EM field) that exist in one meter (1 m) of linear space. Wave number is expressed in reciprocal meters (m-1).

The wave number for an EM field is equal to 2 pi divided by the wavelength in meters. (In some references, it is defined as the reciprocal of the wavelength in meters; in still others, it is defined as the reciprocal of the wavelength in centimeters.) As the wavelength grows shorter, the wave number becomes larger.

Wave number is usually specified for an EM field in a vacuum, also called free space. In most situations, the air is equivalent to a vacuum. In media other than free space, the wave number for a given EM field may increase. When a ray of light passes from air into water or glass, or a radio signal propagates through a polyethylene dielectric rather than air, the wavelength is shortened because the speed of propagation decreases. This causes the wave number to increase.

In free space, the wave number k (in reciprocal meters) is related to the frequency f (in hertz) according to the following formula:

k = f/c

where c is the speed of EM propagation in free space, approximately equal to 2.99792 x 108 meters per second.

In media other than free space, c must be multiplied by a velocity factor v. The velocity factor for a particular medium is the ratio of the speed of EM propagation in that medium to the speed of EM propagation in free space. As such, the velocity factor is always greater than 0 and less than or equal to 1. Taking velocity factor into account, the above formula becomes:

k = f/(vc)

See also EM field, frequency, and wavelength.

This was last updated in September 2005

Start the conversation

Send me notifications when other members comment.

By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy

Please create a username to comment.


File Extensions and File Formats

Powered by:


  • 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. A...

  • 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 ...


  • cloud ecosystem

    A cloud ecosystem is a complex system of interdependent components that all work together to enable cloud services.

  • cloud services

    Cloud services is an umbrella term that may refer to a variety of resources provided over the internet, or to professional ...

  • uncloud (de-cloud)

    The term uncloud describes the action or process of removing applications and data from a cloud computing platform.


  • federated identity management (FIM)

    Federated identity management (FIM) is an arrangement that can be made among multiple enterprises to let subscribers use the same...

  • cross-site scripting (XSS)

    Cross-site scripting (XSS) is a type of injection security attack in which an attacker injects data, such as a malicious script, ...

  • firewall

    In computing, a firewall is software or firmware that enforces a set of rules about what data packets will be allowed to enter or...




  • bad block

    A bad block is an area of storage media that is no longer reliable for storing and retrieving data because it has been physically...

  • all-flash array (AFA)

    An all-flash array (AFA), also known as a solid-state storage disk system, is an external storage array that uses only flash ...

  • volume manager

    A volume manager is software within an operating system (OS) that controls capacity allocation for storage arrays.


  • hybrid hard disk drive (HDD)

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