Polarisation of plane wave:
The polarisation of a plane wave can be defined as the orientation of the electric field vector as a function of time at a fixed point in space. For an electromagnetic wave, the specification of the orientation of the electric field is sufficent as the magnetic field components are related to electric field vector by the Maxwell's equations.
Let us consider a plane wave travelling in the +z direction. The wave has both Ex and Ey components.
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The corresponding magnetic fields are given by,
