The Electro Magnetic Spectrum encompasses a continuous range of frequencies or wavelengths of electro magnetic radiation, ranging from long wave length, low energy radio waves to short wavelength, high frequency, high-energy gamma rays. Frequency is defined as the number of wave cycles that pass a particular point per unit time and is commonly measured in Hertz (cycles per second), wavelength defines the distance between adjacent points of the electro magnetic wave that are in equal phase (wave crests).
German physicist Maxwell Planck proposed that atoms absorb or emit electromagnetic radiation only in certain bundles termed quanta. Albert Einstein used the term photon to describe these electromagnetic quanta. Planck determined that energy of light was proportional to its frequency ie as the frequency of light increases, so does the energy of light.
Although electromagnetic radiation is now understood as having both photon (particle) and wave-like properties, descriptions of the electromagnetic spectrum generally utilizes wave related terminology ie frequency and wavelength.
Electromagnetic fields and photons exert forces that can excite electrons. As electrons transition between allowed orbitals, energy must be conserved. This conservation is achieved by the emission of photons when an electron moves from a higher potential orbital energy to lower potential orbital energy. Accordingly, light is emitted only at certain frequencies characteristic of every atom and molecule. Correspondingly, atoms and molecules absorb only a limited range of frequencies and wavelengths of the electromagnetic spectrum and reflect all other frequencies and wavelengths of light. These reflected frequencies and wavelengths are often the actual observed light or colours associated with an object.
Electromagnetic radiation differ significantly in their properties in their means of production and also in the way we observe then, they have certain other features in common. The following are common features.
(i) They all can be described in terms of oscillating electric (E) and magnetic fields perpendicular to each other and hence are called electromagnetic (E.M) radiation.
(ii) These electric and magnetic fields are found to oscillate perpendicular to the direction of propagation of radiation. All electromagnetic waves are transverse in nature.
(iii) All these radiations travel with the same speed, that is the speed of light (C) in vacuum. The velocity (C) in related to frequency (η) and wavelength (λ).C = ηλ = 3 × 108 m/s
The difference in properties of different types of E.M radiations arise only from the difference in their wavelengths (λ) or frequency (η). Therefore, the name given to particular region of electromagnetic spectrum is based on the range of its wavelengths or frequencies. The variation in the wave lengths of electromagnetic radiation is a continuous one and the various regions overlap and hence are not sharply defined. The energy of electromagnetic radiation. (ie photon) is inversely proportional to wavelength.
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