Features of Electromagnetic Waves

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This diagram shows the key features of electromagnetic (light) waves and introduces some of the terms used to describe them.

  • Across the centre is an electromagnetic wave, shown in red.
  • The wave is travelling from left to right.
  • The different features of the wave are shown by labels.
  • At the bottom of the diagram are short definitions of key terms.

Description

Features of Electromagnetic Waves

TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
The frequency of incident light is unchanged as it travels from air into water and undergoes refraction.
Yes! The wavelength and speed at which light travels change as it travels through different media but frequency remains the same.
The frequency of a wave is a measurement of the number of waves passing a given point in a given time!
Lower frequency = Longer wavelengths.

About the diagram

About the diagram
  • This diagram shows the key features of electromagnetic (light) waves and introduces some of the terms used to describe them.
  • Across the centre is an electromagnetic wave, shown in red.
  • The wave is travelling from left to right.
  • The different features of the wave are shown by labels.
  • At the bottom of the diagram are short definitions of key terms.
Remember that:
  • Electromagnetic radiation (light) is often described in terms of waves.
  • Electromagnetic waves, which are a form of electromagnetic radiation, propagate from a light source, travel through space, and encounter different materials.
  • Visible light corresponds with the range of wavelengths of electromagnetic radiation that are responsible for the sense of sight.
  • Visible light is a form of electromagnetic radiation, as are radio waves, infrared radiation, ultraviolet radiation, X-rays and microwaves.
  • The range of wavelengths that produce visible light forms a very small part of the electromagnetic spectrum.
  • Visible light is perceived as colour. The colour red has been chosen to correspond with the wavelength of this wave.

Some key terms

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.

  • Frequency is measured in Hertz (Hz) and signifies the number of wave-cycles per second. Sub-units of Hertz enable measurements involving a higher count of wave-cycles within a single second.
  • The frequency of electromagnetic radiation spans a broad range, from radio waves with low frequencies to gamma rays with high frequencies.
  • The wavelength and frequency of light are closely linked. Specifically, as the wavelength becomes shorter, the frequency increases correspondingly.
  • It is important not to confuse the frequency of a wave with the speed at which the wave travels or the distance it covers.
  • The energy carried by a light wave intensifies as its oscillations increase in number and its wavelength shortens.

A wave-cycle refers to the path of a wave measured from any point through the course of a single oscillation to the same point on the next oscillation.

  • Imagine a wave-cycle as a series of points marked on the path of the wave between one crest and the next.
  • All electromagnetic waves share features such as crests, troughs, oscillations, wavelength, frequency, amplitude, direction of travel.
  • Whilst a wave-cycle is the path from one point on a wave during a single oscillation to the same point on completion of that oscillation, wavelength is a measurement of the same phenomenon along the axis of the wave.

The speed (or velocity) of a light wave is a measurement of how far it travels in a certain time.

  • The speed of light is measured in metres per second (m/s).
  • Light travels through a vacuum at 300,000 kilometres per second.
  • The exact speed at which light travels through a vacuum is 299,792,458 metres per second.
  • Light travels through other media at lower speeds.
  • A vacuum is a region of space that contains no matter.
  • Matter is anything that has mass and occupies space by having volume.
  • When discussing electromagnetic radiation the term medium (plural media) is used to refer to anything through which light propagates including empty space and any material that occupies space such as a solid, liquid or gas.
  • In other contexts empty space is not considered to be a medium because it does not contain matter.

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.

An electromagnetic wave carries electromagnetic radiation.

  • An electromagnetic wave is formed as electromagnetic radiation propagates from a light source, travels through space and encounters different materials.
  • Electromagnetic waves can be imagined as synchronised oscillations of electric and magnetic fields that propagate at the speed of light in a vacuum.
  • Electromagnetic waves are similar to other types of waves in so far as they can be measured in terms of wavelength, frequency and amplitude.
  • We can feel electromagnetic waves release their energy when sunlight warms our skin.
  • Remember that electromagnetic radiation can be described either as an oscillating wave or as a stream of particles, called photons, which also travel in a wave-like pattern.
  • The notion of waves is often used to describe phenomena such as refraction or reflection whilst the particle analogy is used when dealing with phenomena such as diffraction and interference.

 

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