# Electromagnetic Wave As The Transverse Wave: Phase Factor

**Electromagnetic wave as the transverse wave: phase factor:**** **The factor is termed as the phase factor and plays an important role in determining the status of the wave at any instant of time and or at any location in space. If the phase factor is constant in the transverse plane x-y, than the wave will be called as the plane wave and all the rays in it will be parallel to each other. The planes containing the constant phase are termed as the wavefront. The wave front is perpendicular to the direction of propagation. Fig 2. shows the plane wave front for a plane wave propagating along z axis.

fig..(1) plant wavefront

**Intensity :**The power (energy) associated with the radiation field is measured in terms of intensity I. It is defined in terms of watt/cm^{2}. It is related to the electric field associated with em wave given by

...........................(1)

where is the velocity of propagation of the wave and is the electrical permittivity of the medium through which the wave is propagating.

**Propagation of EM wave: **Electromagnetic waves obeys the Maxwell’s equations.

While talking about the propagation or the transmission of light through a medium without undergoing significant attenuation, then the medium is a dielectric. The Maxwell’s equations for a dielectric medium are given below:

..................(2)

For a linear medium, the displacement vector and (where is the permittivity of the medium).

The equation 1. 4 results into the wave propagation equation given by

............................(3)

From equation 1.5, the velocity of propagation of em wave is given by

....................(4)

If the wave is propagating in vacumm then the free space permitivity and permeability are given by =8.85X10^{-12}s^{2} .C^{2}/m^{2} Kg and =4X10^{-7} m.kg/C^{2} then the speed of light in free space is 3X10 8 m/sec, this normally denoted by c and not v.

Therefore c=3X10^{8} m/sec. The ratio of the speed of light in vacuum to that of in medium is called as the refractive index of the medium n,

.............................(5)

Refractive index of the medium plays an important role in determining the polarization of light through that medium.

To conclude, the basic properties of electromagnetic waves are summed up in this lecture.