Polarisation of light: directions of electric field perpendicular to the directions of wave.magnitude varying sinusoidally with space and time. perpendicular to X -axis there are infinite directions possible in y ,Z and y- z plane.If the electric field at the point always remains parallel to a fixed direction as the time passes the light is called linearly polarized along that direction. the plane containing the electric field and the directions of propagation of wave is called the plane of polarization. the resultant electric field at a point keeps on changing its direction randomly and rapidly is known as unpolarised light. the light emitted by electric lamp a candle, sun is the best example. if phase difference between y component and Z component of electric field varies with time then light is unpolarized . if phase difference is equal to zero then electric field always parallel to fixed direction ,that is linearly polarized . if phase difference is equal to π then resultant electric field again parallel to a fixed direction and light is linear polarization. difference between Y and Z component of electric field is equal to 90 degree or π/2 and Y and Z component of electric field have equal magnitude, then angle θ becomes( ωt- kx ) then at any point θ increases at a uniform rate ω and resultant field becomes equal to E1or E2 then magnitude of the field remains constant . the tip of the electric field does goes in a circle at a uniform angular speed the light is called a circularly polarized light . If phase difference between y and z component of electric field π/2 but E1not equal to E2 then the tip of the electric field goes in an ellipse then light is electrically elliptically polarised light.