Reading Comprehension Related

Review Reading Comprehension related questions and content

Doppler Effect
Have you ever wondered why the whistle of a traveling, distant locomotive predicts its approach several yards before anyone actually sees it? Or why an oncoming ambulance's screaming siren is heard momentarily several feet before the ambulance comes into full view, before it passes you, and why its siren is still heard faintly well after the ambulance is out of sight?
What you are witnessing is a scientific phenomenon known as the Doppler Effect. What takes place is truly remarkable. In both of these instances, when the train or ambulance moves toward the sound waves in front of it, the sound waves are pulled closer together and have a higher frequency. In either instance, the listener positioned in front of the moving object hears a higher pitch. The ambulance and locomotive are progressively moving away from the sound waves behind them, causing the waves to be farther apart and to have a lower frequency. These fast-approaching modes of transportation distance themselves past the listener, who hears a lower pitch.

Which sound waves have a lower pitch?

  • A. Sound waves that are closer together
  • B. Sound waves that are farther apart
  • C. Sound waves that travel a long distance
  • D. Sound waves that travel a short distance
Correct Answer: B

Rationale: Sound waves that are farther apart have a lower pitch. In the Doppler Effect, as a source of sound moves away from a listener, the sound waves get stretched out, causing a decrease in frequency and resulting in a lower pitch. Conversely, when a source of sound moves toward a listener, the sound waves get compressed, leading to an increase in frequency and a higher pitch. This phenomenon explains why the pitch of sound changes depending on whether the source is moving towards or away from the listener.