Electromagnetic Spectrum
Electromagnetic Spectrum; The areas of Optical sciences normally refer to a small spectral region of electromagnetic radiation. Normally it covers the region from UV to IR region. Every part of electromagnetic spectrum has one or more than one application. Some of the common applications of the various regions of electromagnetic spectrum are listed below :
Gamma Rays:

XRays:

ULF:
10^{2}  10^{3}

Audio, Telephone 
Electromagnetic wave as the transverse wave :
It is well known fact that the electromagnetic radiation behaves as the transverse wave.
Thus the light behaves as transverse waves. This means that the electric and magnetic field disturbances are in the plane transverse to the direction of propagation of the wave. Electric and magnetic fields are also perpendicular to each other and are interrelated also.
Essential parameters of Electromagnetic wave:
For complete mathematical representation of the electromagnetic wave it is sufficient to know the following:
(a) Frequency of the wave or angular frequency : A fundamental property of the wave, so long it is propagating through a linear medium.
(b) Amplitude and the direction of electric field E_{0} :
(c) Propagation vector k whose magnitude is (c being the velocity of propagation of the em wave and its direction represents the direction of propagation of the em wave).
For a pure monochromatic wave moving along the zaxis (also called as the longitudinal direction), the electric field can be written as
Thus at any given time t , the variation of the electric field along the longitudinal direction is sinusoidal as shown in fig 1(a). The variation of electric field at a particular location z as a function of time t is also sinusoidal as shown in fig 1(b).
The relation between electric field and the magnetic field for an electromagnetic wave is given by
.....(1.2) Thus equation 1.1 is a complete description of the electromagnetic wave described with the help of three parameters defined, above