The polarization of an electromagnetic wave refers to the orientation of the electric field vector as the wave propagates through space. There are three types of polarization: linear polarization, circular polarization, and elliptical polarization. In this case, when the phase angle between the Ex and Ey components is 0° or 180°, the polarization is linear.

Explanation:
- Linear polarization: In linearly polarized waves, the electric field vector oscillates in a single plane as the wave propagates. This plane is perpendicular to the direction of wave propagation. The electric field vector can be represented by two orthogonal components, Ex and Ey, which are in phase with each other.
- Phase angle between Ex and Ey: The phase angle between Ex and Ey determines the relative timing of their oscillations. It represents the phase difference between the two components and is measured in degrees. When the phase angle is 0° or 180°, it means that the two components are perfectly in phase or completely out of phase.
- When the phase angle is 0°: In this case, the Ex and Ey components have the same phase and oscillate in perfect synchrony. As a result, the electric field vector traces a straight line in a fixed direction as the wave propagates. This represents linear polarization.
- When the phase angle is 180°: In this case, the Ex and Ey components have opposite phases and oscillate in anti-phase. As a result, the electric field vector still traces a straight line, but in the opposite direction from the previous case. This also represents linear polarization.
- Other polarization types: Circular polarization occurs when the phase angle is 90° or 270°, resulting in the electric field vector rotating in a circular pattern as the wave propagates. Elliptical polarization occurs when the phase angle is any value other than 0°, 90°, 180°, or 270°, resulting in the electric field vector tracing an elliptical pattern.
- Conclusion: When the phase angle between the Ex and Ey components is 0° or 180°, the polarization is linear because the electric field vector oscillates in a single plane, either in the same direction or in the opposite direction as the wave propagates.