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Read the following statements about the properties of electromagnetic waves and identify the correct ones. A. In a plane EM wave the electric and magnetic fields are mutually perpendicular, and the direction of propagation lies along either the electric or the magnetic field. B. The energy of an EM wave is shared equally between its electric and magnetic fields. C. The electric and magnetic fields are parallel to each other and both perpendicular to the propagation direction. D. The electric field, the magnetic field and the propagation direction are all mutually perpendicular. E. The ratio of the magnetic-field amplitude to the electric-field amplitude equals the speed of light. Choose the most appropriate option.

1. D only
2. B and D only
3. B, C and E only
4. A, B and E only

Correct answer: B and D only

Solution

D is correct: E, B and the propagation direction are mutually perpendicular. B is correct: average energy is split equally between the electric and magnetic fields. A is wrong because propagation is perpendicular to both fields, not along them. C is wrong because E and B are perpendicular, not parallel. E is wrong because E0/B0 = c, so B0/E0 = 1/c, not c. Hence only B and D are correct.

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