Electromagnetic Spectrum


This diagram shows that the electromagnetic spectrum includes waves with all possible wavelengths, ranging from low energy radio waves through visible light to high energy gamma rays.

Remember that:


Electromagnetic spectrum

The frequency of incident light is unchanged as it travels from air into water and undergoes refraction.
The frequency of incident light is unchanged as it travels from air into glass so its colour remains the same.
The frequency of a wave is a measurement of the number of waves passing a given point in a given period of time!

About the diagram

About the diagram
  • This diagram shows that the electromagnetic spectrum includes waves with all possible wavelengths, ranging from low energy radio waves through visible light to high energy gamma rays.
  • Notice that a wave with a longer wavelength has a lower frequency and carries less energy.
  • Notice that a wave with a shorter wavelength has a higher frequency and carries more energy.
Remember that:
  • The electromagnetic spectrum includes, in order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
  • There are no precisely defined boundaries between the bands of electromagnetic radiation in the electromagnetic spectrum. Each band is associated with different properties and applications – think of radios, microwaves, x-ray machines etc.
  • Visible light is only a very small part of the electromagnetic spectrum.
  • Energy (electromagnetic energy) is the radiant energy (light) transported by electromagnetic waves.
  • The term light can be used in three different ways:
    • Light can be used to mean the whole of the electromagnetic spectrum from radio waves, through visible light to gamma rays. A better term is radiant energy or photon energy.
    • Light can be used to mean the range of wavelengths and frequencies that can be detected by the human eye. A better term is visible light which refers to the wavelengths that correspond with the colours between red and violet, the visible spectrum.
    • Light can be used to mean the range of wavelengths and frequencies between infra-red and ultra-violet. This usage is useful because the outer limits of the visible spectrum change under different lighting conditions and for different individuals.
  • Referring to visible light simply as light is short-hand.
  • Visible light is not the same for all living things.

Some key terms

Wavelength is a measurement from any point on the path of a wave to the same point on its next oscillation. The measurement is made parallel to the centre-line of the wave.

  • The wavelength of an electromagnetic wave is measured in metres.
  • Each type of electromagnetic radiation, such as radio waves, visible light and gamma waves,  forms a band of wavelengths on the electromagnetic spectrum.
  • The visible part of the electromagnetic spectrum is composed of the range of wavelengths that correspond with all the different colours we see in the world.
  • Human beings don’t see wavelengths of visible light, but they do see the spectral colours that correspond with each wavelength and the other colours produced when different wavelengths are combined.
  • The wavelength of visible light is measured in nanometres. There are 1,000,000,000 nanometres to a metre.

The frequency of electromagnetic radiation (light) refers to the number of wave-cycles of an electromagnetic wave that pass a given point in a given amount of time.

A nanometre is a unit of measurement of the wavelength of electromagnetic radiation.

An electronvolt is a unit of energy commonly used to measure the energy carried by electromagnetic radiation.

  • Electronvolts can be used for measurements at the scale of elementary particles as small as single photons, the quantum of the electromagnetic field.
  • One electronvolt is the amount of energy that a single electron has when it is accelerated by a potential difference of 1 volt.
  • If there is a difference in voltage of 1 volt between two points in an electrical circuit (within a capacitor for example) then the force required (and the energy gained) by a photon accelerating from one point to the other is 1 electronvolt.

The hertz (symbol: Hz) is a unit used to measure the frequency of electromagnetic waves.

    • 1 Hertz (Hz) = 1 cycle per second
    • 1 Kilohertz (kHz) = 1,000 (thousand) cycles per second
    • 1 Megahertz (MHz) = 1,000,000 (million) cycles per second
    • 1 Gigahertz (GHz) = 1,000,000,000 (billion) cycles per second
    • 1 Terahertz (THz) = 1,000,000,000,000 (trillion )cycles per second

Energy is a property of matter.

  • Everything contains energy including all forms of matter and so all objects.
  • Energy is evident in all forms of movement, interactions between, and changes to the forms and properties of matter.
  • At an atomic level, energy is evident in the movement of electrons around the nucleus of an atom. Energy is stored in the nucleus of atoms as a result of the forces that bind protons and neutrons together.
  • Energy can be transferred between objects, and converted from one form to another, but cannot be created or destroyed.
  • Everything in the universe uses energy in one form or another.
  • When it comes down to it, matter is energy.
  • Light has energy but no mass so does not occupy space and has no volume.
  • Energy is often described as either being potential energy or kinetic energy.
  • Energy is measured in joules.

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