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.

See a brief introduction to the history of light:

This was last updated in November 2015

Continue Reading About photon

Join the conversation

3 comments

Send me notifications when other members comment.

Please create a username to comment.

its great...
Cancel
If  photon had mass would it lose speed in a reverse venture?
Cancel
If a photo had mass would it lose velocity in a reverse venture? 
Cancel

-ADS BY GOOGLE

File Extensions and File Formats

Powered by:

SearchCompliance

  • compliance framework

    A compliance framework is a structured set of guidelines that details an organization's processes for maintaining accordance with...

  • regulatory compliance

    Regulatory compliance is an organization's adherence to laws, regulations, guidelines and specifications relevant to its business...

  • privacy compliance

    Privacy compliance is a company's accordance with established personal information protection guidelines, specifications or ...

SearchSecurity

SearchHealthIT

  • telemedicine (telehealth)

    Telemedicine is the remote delivery of healthcare services, such as health assessments or consultations, over the ...

  • Project Nightingale

    Project Nightingale is a controversial partnership between Google and Ascension, the second largest health system in the United ...

  • medical practice management (MPM) software

    Medical practice management (MPM) software is a collection of computerized services used by healthcare professionals and ...

SearchDisasterRecovery

  • crisis management plan (CMP)

    A crisis management plan (CMP) outlines how to respond to a critical situation that would negatively affect an organization's ...

  • disaster recovery (DR) test

    A disaster recovery test (DR test) is the examination of each step in a disaster recovery plan as outlined in an organization's ...

  • business continuity plan (BCP)

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

SearchStorage

  • kilobyte (KB or Kbyte)

    A kilobyte (KB or Kbyte) is a unit of measurement for computer memory or data storage used by mathematics and computer science ...

  • megabytes per second (MBps)

    Megabytes per second (MBps) is a unit of measurement for data transfer speed to and from a computer storage device.

  • zettabyte

    A zettabyte is a unit of measurement used by technology professionals and the general public to describe a computer or other ...

Close