Browse Definitions :
Definition

photon

The photon is the fundamental particle of visible light.

In some ways, visible light behaves like a wave phenomenon, but in other respects it acts like a stream of high-speed, submicroscopic particles. Isaac Newton was one of the first scientists to theorize that light consists of particles. Modern physicists have demonstrated that the energy in any electromagnetic field is made up of discrete packets. The term photon (meaning "visible-light particle") was coined for these energy packets. Particle-like behavior is not restricted to the visible-light portion of the electromagnetic radiation spectrum, however. Radio waves, infrared rays, visible light, ultraviolet rays, X rays, and gamma rays all consist of photons, each of which contains a particular amount of energy that depends on the wavelength.

Photons travel through empty space at a speed of approximately 186,282miles (299,792 kilometers) per second. This is true no matter what the electromagnetic wavelength. In media other than a vacuum, the speed is reduced. For example, visible light travels more slowly through glass than through outer space. Radio waves travel more slowly through the polyethylene in a transmission line than they do through the atmosphere. The ratio of the speed of the photons in a particular medium to their speed in a vacuum is called the velocity factor . This factor is always between 0 and 1 (or 0 and 100 percent), and it depends to some extent on the wavelength.

The shorter the wavelength of an electromagnetic disturbance, the more energy each photon contains. In fact, this relationship is so precise that a mathematical formula applies. If e represents the energy (the unit of measurement is the joule) contained in each photon and s represents the electromagnetic wavelength (in meters), then

e = hc / s

where h is Planck's constant (approximately equal to6.626 times 10 -34 joule-second) and c is the speed of electromagnetic-field propagation in the medium in question (approximately 2.998 times 10 8 meters per second in a vacuum). A simpler formula applies to frequency. If f represents the frequency of an electromagnetic field (in hertz), then

e = hf

The energy contained in a single photon does not depend on the intensity of the radiation. At any specific wavelength -- say, the wavelength of light emitted by a helium-neon laser -- every photon contains exactly the same amount of energy, whether the source appears as dim as a candle or as bright as the sun. The brilliance or intensity is a function of the number of photons striking a given surface area per unit time.

This was last updated in November 2015

Continue Reading About photon

SearchNetworking
  • virtual network functions (VNFs)

    Virtual network functions (VNFs) are virtualized tasks formerly carried out by proprietary, dedicated hardware.

  • network functions virtualization (NFV)

    Network functions virtualization (NFV) is a network architecture model designed to virtualize network services that have ...

  • overlay network

    An overlay network is a virtual or logical network that is created on top of an existing physical network.

SearchSecurity
  • X.509 certificate

    An X.509 certificate is a digital certificate that uses the widely accepted international X.509 public key infrastructure (PKI) ...

  • directory traversal

    Directory traversal is a type of HTTP exploit in which a hacker uses the software on a web server to access data in a directory ...

  • malware

    Malware, or malicious software, is any program or file that is intentionally harmful to a computer, network or server.

SearchCIO
  • chief transformation officer (CTO)

    Chief transformation officer is an executive role, often in the C-suite, that focuses on bringing about change as well as growth ...

  • data latency

    Data latency is the time it takes for data packets to be stored or retrieved. In business intelligence (BI), data latency is how ...

  • chief data officer (CDO)

    A chief data officer (CDO) in many organizations is a C-level executive whose position has evolved into a range of strategic data...

SearchHRSoftware
SearchCustomerExperience
  • implementation

    Implementation is the execution or practice of a plan, a method or any design, idea, model, specification, standard or policy for...

  • first call resolution (FCR)

    First call resolution (FCR) is when customer service agents properly address a customer's needs the first time they call.

  • customer intelligence (CI)

    Customer intelligence (CI) is the process of collecting and analyzing detailed customer data from internal and external sources ...

Close