How do electric and magnetic fields behave in a radio wave?

How do electric and magnetic fields behave in a radio wave?

• A. They travel separately at different speeds
• B. They propagate independently without energy transfer
• C. They support each other and propagate through space at the speed of light
• D. They only exist near the source

Answer: (C)

In a radio wave the electric and magnetic fields are inseparable parts of a single electromagnetic disturbance that travels through space together at the speed of light. As the wave propagates, the changing magnetic field generates an electric field and the changing electric field generates a magnetic field, so the wave keeps sustaining itself without needing a medium. The fields are perpendicular to each other and to the direction of travel, and they reach the observer in phase, so energy flows along the propagation direction. This energy transfer is described by the Poynting vector, S = E × B/μ0. In free space the magnitudes relate by E = cB, with c being the speed of light, and c = fλ linking frequency and wavelength. These waves radiate away from the source, carrying energy and information, not confined to the vicinity of the source.

In a radio wave the electric and magnetic fields are inseparable parts of a single electromagnetic disturbance that travels through space together at the speed of light. As the wave propagates, the changing magnetic field generates an electric field and the changing electric field generates a magnetic field, so the wave keeps sustaining itself without needing a medium. The fields are perpendicular to each other and to the direction of travel, and they reach the observer in phase, so energy flows along the propagation direction. This energy transfer is described by the Poynting vector, S = E × B/μ0. In free space the magnitudes relate by E = cB, with c being the speed of light, and c = fλ linking frequency and wavelength. These waves radiate away from the source, carrying energy and information, not confined to the vicinity of the source.