Comparing Frequencies of Red & Violet



Comparing Frequencies of Red and Violet

The hertz is used to measure the frequency of electromagnetic waves. Different prefixes denoting subdivisions are used to aid measurement eg. kilohertz (1,000 cycles/sec), megahertz ( 1,000,000 cycles/sec), gigahertz (1,000,000,000 cycles/sec) and terahertz (1,000,000,000,000 cycles/sec).
Shorter wavelengths = Higher frequency.
The frequency of incident light is unchanged as it travels from air into water and undergoes refraction.
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 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

Electromagnetic wave

An electromagnetic wave carries electromagnetic radiation. An electromagnetic wave is formed as electromagnetic radiation propagates from a light source, travels ...

Visible spectrum

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


Wavelength is a measurement from any point on the path of a wave to the same point on its next ...

Electromagnetic spectrum

The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths of electromagnetic radiation, ranging from low energy radio waves through ...

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