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

(d) 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.