What is light?

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  • A form of energy that the Sun emits in all directions

Properties of Light

  • Light travels in straight lines:
  • Light travels VERY FAST – around 300,000, 000 metres per second. (3.0 x 108 m/s)
  • Light travels much faster than sound. For example: Light energy is transferred through radiation

RADIATION

  • A method of energy transfer that does not require a medium

MEDIUM

  • Any physical substance that acts as a carrier for the transmission of energy
    • Light is an electromagnetic wave
  • Electromagnetic waves are based on the
    energy of waves.
  • We use the electromagnetic spectrum as the classification system.
  • The electromagnetic spectrum is the complete spectrum  or continuum of light.

Radio waves

  • Low energy waves with long wavelengths
  • Includes FM, AM, radar and TV waves
  • Low frequency
  • Used in many devices such as remote control items, cell phones, wireless devices, etc.

Microwaves

  • Longer than radio, shorter than light and infrared
  • First used in radar, now used in communication, medicine and consumer use (microwave ovens)

Infrared light

  • Invisible waves that are detected as heat
  • Can be detected with special devices such as night goggles
  • Used in heat lamps, remote controls, lasers
  • Higher energy than microwaves but lower than visible light

Visible Light

  • The portion of the electromagnetic spectrum that human eyes can detect
  • ROYGBIV (red, orange, yellow, green, blue, indigo, violet)
  • Red is the lowest frequency and violet is the highest frequency
  • White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow.
  • The colour sequence is the visible spectrum

Ultraviolet waves

  • Higher energy than light waves
  • Causes skin to tan and burn
  • Can cause skin cancer and blindness in humans
  • Used in tanning beds and sterilizing equipment
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X-Rays

  • Medical imaging (i.e. used for teeth and bones)
  • Security equipment (i.e. luggage scanners)
  • High energy waves
  • Can cause cancer

Gamma rays

  • Highest energy
  • Generated by radioactive atoms and in nuclear explosions.
  • Can kill living cells
  • Gamma rays are used to kill cancerous cells.
  • Blocked from Earth’s
  • surface by atmosphere

Sources of Light

  • Luminous and non-luminous objects
  • We see things because they reflect light into our eyes:

Shadows

  • Sources of Light (Luminous)

Incandescence

  • is the emission of light (visible electromagnetic radiation) as a result of high temperature.

Electric Discharge

  • Produced by an electric current passing through a gas
  • Different gases produce different colours
  • Examples of electric discharge:
    • lightning, neon sign
    • Examples of gases:
      • neon gas produces red colour;
      • helium produces gold-colour
      • argon produces a pale violet-blue

Fluorescence

  • An object absorbs ultraviolet light and immediately releases the energy as visible light.
  • Sources of Light

Phosphorescence

  • It is the process of producing light by the absorption of ultraviolet light
  • It is the emission of visible light over an extended period of time. It can range from seconds to days
  • Sources of Light

Chemiluminescence (sometimes “cold light”)

  • is the emission of light with limited emission of heat (luminescence), as the result of a chemical reaction.
  • Sources of Light

Bioluminescence

  • is the production and emission of light by a living organism.
  • the result of a chemical reaction with little or no heat produced.
  • Sources of Light

Triboluminescence

  • is the production of light from friction as a result of scratching, crushing, or rubbing certain crystals through the breaking of chemical bonds in the material.
  • Sources of Light

Light from Light-Emitting Diode (LED)

  • An electronic device that allows an electric current to flow in only one direction.
  • It does not require a filament.
  • It does not produce much heat.
  • Energy efficient

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