Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Electromagnetic (EM) radiation is a self-propagating wave in space or through matter.
Electromagnetic radiation consists of discrete packets of energy, which we call photons. A photon consists of an oscillating electric field component, E, and an oscillating magnetic field component, M.
The electric and magnetic fields are orthogonal (perpendicular) to each other, and they are orthogonal to the direction of propogation of the photon. The electric and magnetic fields of a photon flip direction as the photon travels.
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The number of flips or oscillations, that occur in one second is known as the frequency. Frequency has the units of oscillations per second or simply s”1 (this unit is given the name Hertz).
Electromagnetic radiation is classified into types according to the frequency of the wave, these types include (in order of increasing frequency): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
Of these, radio waves have the longest wavelengths and Gamma rays have the shortest. EM radiation carries energy and momentum, which may be imparted when it interacts with matter.
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All photons (in a given, non-absorbing medium) travel at the same velocity, (v). The physical distance in the direction of propogation over which the electric and magnetic fields of a photon make one complete oscillation is called the wavelength, (A), of the electromagnetic radiation.
The electromagnetic nature of all photons is the same, but photons can have different frequencies. The names we give electromagnetic radiation for different wavelength and frequency ranges are listed in the electromagnetic spectrum document. The energy, E, of one photon depends on its frequency of oscillation:
E =hv/λ
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Where h is Planck’s constant (6.62618 × 10-34 J.s).
Electromagnetic waves travel through a vacuum at a constant velocity of 2.99792 × 108 m/s, which is known as the speed of light, (c).