What describes the Doppler Effect?

• A. Change in direction of a wave
• B. Change in wavelength due to a moving observer
• C. Increase in light speed in a vacuum
• D. Constant frequency of waves regardless of movement

Answer: (B)

The Doppler Effect refers to the change in frequency and wavelength of a wave in relation to an observer moving relative to the source of the wave. When the source of a wave (such as sound, light, or electromagnetic waves) moves toward an observer, the waves are compressed, which leads to a decrease in wavelength and an increase in frequency. Conversely, if the source is moving away from the observer, the waves are stretched, resulting in an increase in wavelength and a decrease in frequency.

Thus, the correct answer accurately captures this phenomenon by emphasizing the change in wavelength that results from the movement of the observer in relation to the wave source. This effect is commonly experienced in everyday life; for example, the change in pitch of a siren from an ambulance as it approaches and then passes by is a real-world demonstration of the Doppler Effect.

The other options do not appropriately describe this phenomenon, as they either address irrelevant concepts or incorrectly characterize the nature of wave behavior in relation to movement.