Comparing Frequencies of Red & Violet

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This diagram compares the frequency of two electromagnetic waves that correspond with an observer’s perception of red and violet.


The diagram shows that the frequency of electromagnetic waves (light) refers to the number of oscillations that pass a given point in a given amount of time.

Understanding the diagram

  • The diagram shows a total of three wave-cycles for red and eight wave-cycles for violet. The length of one wave-cycle (oscillation) is shown as a yellow arrow drawn on each wave.
  • The point at which measurement of passing waves is taken is shown as a vertical line below a clock face whilst the period of time is shown as an arrow.
  • During the measurement period, one red wave and three violet waves pass the measurement point. So the frequency of violet is 3 wave-cycles and the frequency of red is 1 wave-cycle.
  • Because red has fewer wave-cycles per second than violet it is said to have a lower frequency.
  • Because violet has more wave-cycles per second than red it is said to have a higher frequency.
  • Because the frequency of electromagnetic waves in the visible part of the spectrum is so high the diagram shows the difference between Hertz, Kilohertz, Megahertz and Gigahertz and Terahertz.

Description

Comparing Frequencies of Red and Violet

TRY SOME QUICK QUESTIONS AND ANSWERS TO GET STARTED
The frequency of an electromagnetic wave is a measurement of the number of wave oscillations passing a given point in a given period of time.
Shorter wavelengths = Higher frequency.
The frequency of incident light is unchanged as it travels from air into water and undergoes refraction.

About the diagram

About the diagram
  • This diagram compares the frequency of two electromagnetic waves that correspond with an observer’s perception of red and violet. It also looks at the units used when frequency is being measured.
  • The diagram shows that the frequency of electromagnetic waves (light) refers to the number of oscillations that pass a given point in a given amount of time.
Understanding the diagram
  • The diagram shows a total of three wave-cycles for red and eight wave-cycles for violet. The length of one wave-cycle (oscillation) is shown as a yellow arrow drawn on each wave.
  • The point at which measurement of passing waves is taken is shown as a vertical line below a clock face whilst the period of time is shown as an arrow.
  • During the measurement period, one red wave and three violet waves pass the measurement point. So the frequency of violet is 3 wave-cycles and the frequency of red is 1 wave-cycle.
  • Because red has fewer wave-cycles per second than violet it is said to have a lower frequency.
  • Because violet has more wave-cycles per second than red it is said to have a higher frequency.
  • Because the frequency of electromagnetic waves in the visible part of the spectrum is so high the diagram shows the difference between Hertz, Kilohertz, Megahertz and Gigahertz and Terahertz.
Remember that:
  • The frequency of a wave should not be confused with the speed at which the wave travels or the distance it travels.
  • The term frequency refers to the measurement of the frequency of wave oscillations that pass a given point in a given amount of time.
  • The unit of measurement of frequency is the hertz. One hertz is one wave-cycle per second.
  • Because the frequency of electromagnetic waves is so small, Hertz is sub-divided into kilohertz, megahertz, gigahertz and terahertz.
  • The number of each unit per hertz is shown in the diagram.
  • The wavelength and frequency of light are closely related. In any given medium, the higher the frequency, the shorter the wavelength.
  • The amount of energy transported by a light wave increases with the frequency of oscillations (wave-cycle) and as the length of each oscillation decreases.
Remember also:
  • The position of an electromagnetic wave within the electromagnetic spectrum is determined by its frequency or wavelength.
  • 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.
  • The electromagnetic spectrum includes all possible frequencies of electromagnetic radiation, ranging from low energy radio waves through visible light up to high energy gamma rays.
  • The full range of frequencies of visible light, between red and violet, is called the visible spectrum.

Some key terms

An electromagnetic wave carries electromagnetic radiation.

The visible part of the electromagnetic spectrum is called the visible spectrum.

  • The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.
  • As light travels through the air it is invisible to our eyes.
  • Human beings don’t see wavelengths of light, but they do see the spectral colours that correspond with each wavelength and colours produced when different wavelengths are combined.
  • The visible spectrum includes all the spectral colours between red and violet and each is produced by a single wavelength.
  • The visible spectrum is often divided into named colours, though any division of this kind is somewhat arbitrary.
  • Traditional colours referred to in English include red, orange, yellow, green, blue, and violet.

Wavelength measures a complete wave cycle, which is the distance from any point on a wave to the corresponding point on the next wave.

  • While wavelength can be measured from any point on a wave, it is often simplest to measure from the peak of one wave to the peak of the next or from the bottom of one trough to the bottom of the next, ensuring the measurement covers the whole of the cycle.
  • The wavelength of an electromagnetic wave is usually given in metres.
  • The wavelength of visible light is typically measured in nanometres, with 1,000,000,000 nanometres making up a metre.
  • Radio waves, visible light, and gamma waves for example, each have different ranges of wavelengths within the electromagnetic spectrum.

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 is the complete up-and-down motion of a wave, from one crest (peak) to the next crest, or from one trough (dip) to the next trough. Visualize a wave cycle as a series of points plotted along the path of a wave from one crest to the subsequent crest.

  • All electromagnetic waves have common characteristics like crests, troughs,, wavelength, frequency, amplitude, and propagation direction.
  • As a wave vibrates, a wave-cycle can be seen as a sequence of individual vibrations, measured from one peak to the next, one trough to the next, or from the start of one wave cycle to the start of the next.
  • A wave-cycle refers to the path from one point on a wave during a single oscillation to the same point on completion of that oscillation.
  • Wavelength meanwhile, is a measurement of the same phenomenon but in a straight line along the axis of the wave.

The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world.

  • As light travels through the air it is invisible to our eyes.
  • Human beings don’t see wavelengths of light, but they do see the spectral colours that correspond with each wavelength and colours produced when different wavelengths are combined.
  • The visible spectrum includes all the spectral colours between red and violet and each is produced by a single wavelength.
  • The visible spectrum is often divided into named colours, though any division of this kind is somewhat arbitrary.
  • Traditional colours referred to in English include red, orange, yellow, green, blue, and violet.

The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths of electromagnetic radiation, ranging from low-energy radio waves through visible light to high-energy gamma rays.

  • There are no precisely defined boundaries between the bands of electromagnetic radiation in the electromagnetic spectrum.
  • 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.
  • Visible light is only a very small part of the electromagnetic spectrum.

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