Question 15

The Doppler Effect explains why sound is heard more strongly initially and then faintly after a moving object has passed.

The passage primarily focuses on the Doppler Effect, illustrating how sound waves behave as moving objects travel toward and away from a listener. It explains that as these objects approach, the frequency of the sound increases, resulting in a higher pitch, and as they move away, the frequency decreases, leading to a lower pitch.

A) Trains and ambulances produce specific sounds

While trains and ambulances are mentioned in the passage, this option does not capture the main idea. The focus is not merely on the sounds produced by these vehicles, but rather on the scientific explanation behind how their motion affects the perception of sound.

B) Low-frequency waves produce high-pitched sounds.

This statement is incorrect as it misrepresents the relationship between frequency and pitch. The passage explains that high-frequency waves produce higher-pitched sounds, not low-frequency waves. Therefore, this option fails to align with the core concept discussed.

C) High-frequency waves produce low-pitched sounds.

This option is also incorrect because it contradicts the information in the passage. The text explicitly states that high-frequency sound waves result in higher-pitched sounds, not low-pitched. Thus, this statement does not reflect the passage's main idea.

D) The Doppler Effect explains why sound is heard more strongly initially and then faintly after a moving object has passed.

This option accurately encapsulates the main idea of the passage. It highlights the Doppler Effect and explains how the perception of sound changes as a moving object approaches and then moves away from the listener, which is the primary focus of the text.

Conclusion

The correct answer, D, effectively summarizes the main idea of the passage by connecting the Doppler Effect to the experience of hearing sounds from moving objects. Options A, B, and C fail to address the scientific principle being discussed and do not capture the essence of how sound perception changes with motion, making them incorrect.