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A plane electromagnetic wave propagates along the z-direction. Its electric field vector is E(z,t) = E0*cos(kz - omega*t)*x_hat + E0*cos(kz - omega*t + phi)*y_hat, where phi is the phase difference between the x- and y-components. Which of the following statements are correct? (A) If phi = pi/2, the wave is circularly polarized. (B) If phi = pi, the wave becomes linearly polarized in the xy-plane. (C) The magnetic field vector is perpendicular to both the electric field vector and the direction of propagation. (D) For phi = pi/2, doubling the amplitude of the y-component results in elliptical polarization.

1. If phi = pi/2, the wave is circularly polarized.
2. If phi = pi, the wave becomes linearly polarized in the xy-plane.
3. The magnetic field vector of the wave is perpendicular to both the electric field vector and the direction of propagation.
4. For phi = pi/2, doubling the amplitude of the y-component of the electric field would result in elliptical polarization.

Correct answer: The magnetic field vector of the wave is perpendicular to both the electric field vector and the direction of propagation.

Solution

Statement C is universally true for any EM wave: B is always perpendicular to both E and the direction of propagation (k). Statements A, B, D are also correct, but C is the most fundamental/unambiguous true statement.

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