MCAT这些物理不花时间复习，想不费力真的不行

其他不敢提插不上嘴，物理自己懂。本想批评娃的，但一看MCAT这些物理没花时间复习真的不行。

这道题算简单直白的问题，让我答也答不对。真想不通学文科的学点物理能回答吗？

Question 11

Which of the following explains why the pitch of person’s resonant voice harmonics rises when they inhale helium instead of air?

A.

The wavelength increases due to the change in temperature from the helium atoms.

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B.

The change in timbre results in a higher perceived frequency of the voice.

Explanation：The pitch of a perceived sound is dependent on its frequency. In the case of the human voice, there are many overlapping waves with various frequencies and higher harmonics of those frequencies. Nonetheless, the basic fact remains that pitch depends on perceived frequency. Thus, when helium atoms are inhaled, the density of the air is being changed, which alters the timbre (an overall quality of voice that results from overlapping waves) to emphasize the higher-pitched harmonics. We perceive that as a high-pitched, "squeaky" voice. However, note that even without knowing the definition of timbre, this question can be solved by eliminating the other options.

C.

The frequency decreases due to the change in air density from helium atoms.

A decrease in frequency would result in a lower-pitched, deeper voice, not a high-pitched squeaky voice.

D.

The speed of the sound wave remains constant regardless of changes to the medium through which the sound wave propagates.

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