Calculating the Frequency of EM Waves


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Calculating the Frequency of EM Waves

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).
The frequency of incident light is unchanged as it travels from air into water and undergoes refraction.

About the diagram

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.

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.

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.

An electromagnetic wave carries electromagnetic radiation.

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

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.

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