What are the common polarization states of an electromagnetic plane wave and how are they defined?

What are the common polarization states of an electromagnetic plane wave and how are they defined?

• A. Linear polarization: E remains in a fixed plane; Circular polarization: E rotates with constant magnitude; Elliptical polarization: E traces an ellipse.
• B. Linear polarization: E rotates with constant magnitude; Circular polarization: E remains in a fixed plane; Elliptical polarization: E traces an ellipse.
• C. Linear polarization: E remains in a fixed plane; Circular polarization: E rotates with constant magnitude; Elliptical polarization: E traces an ellipse.
• D. Linear polarization: E magnitude remains constant; Circular polarization: E rotates with time while magnitude changes; Elliptical polarization: E is zero.

Answer: (C)

Polarization describes how the electric field vector at a fixed point moves in time as the wave passes. For a plane wave, the field is transverse, so its tip moves in the plane perpendicular to the direction of travel. In linear polarization, the two orthogonal components combine to give a resultant field that points along a fixed direction in that transverse plane. The tip of the electric field therefore traces a straight line as time varies. In circular polarization, the two transverse components have equal amplitudes but a 90-degree phase difference. This causes the tip of the electric field to rotate smoothly with time, maintaining a constant magnitude; it traces a circle. In elliptical polarization, the amplitudes and/or phase difference are such that the tip follows an ellipse. The instantaneous magnitude generally changes over time, and the path is not a straight line or a circle. So the best description matches linear polarization as remaining in a fixed direction (or fixed plane in the transverse context), circular polarization as rotating with constant magnitude, and elliptical polarization as tracing an ellipse.

Polarization describes how the electric field vector at a fixed point moves in time as the wave passes. For a plane wave, the field is transverse, so its tip moves in the plane perpendicular to the direction of travel.

In linear polarization, the two orthogonal components combine to give a resultant field that points along a fixed direction in that transverse plane. The tip of the electric field therefore traces a straight line as time varies.

In circular polarization, the two transverse components have equal amplitudes but a 90-degree phase difference. This causes the tip of the electric field to rotate smoothly with time, maintaining a constant magnitude; it traces a circle.

In elliptical polarization, the amplitudes and/or phase difference are such that the tip follows an ellipse. The instantaneous magnitude generally changes over time, and the path is not a straight line or a circle.

So the best description matches linear polarization as remaining in a fixed direction (or fixed plane in the transverse context), circular polarization as rotating with constant magnitude, and elliptical polarization as tracing an ellipse.