MCAT Physics Question 92: Answer and Explanation

Home > MCAT Test > MCAT physics practice tests

Test Information

Question: 92

2. A child is practicing the first overtone on his flute. If his brother covers one end of the flute for a brief second, how will the sound change, assuming that the new pitch represents the first overtone in the new setup?

  • A. The pitch of the sound will go up.
  • B. The pitch of the sound will go down.
  • C. The pitch of the sound will not change.
  • D. The change in the pitch depends on the starting pitch.

Correct Answer: B

Explanation:

This question is testing our understanding of pipes open at one or both ends. To begin, remember that high-frequency sounds have a high pitch and low-frequency sounds have a low pitch. The pipe in this example begins as one that is open on both ends, and then one end is closed off. Our task, therefore, is to determine how the frequency of the second harmonic differs between a pipe that is open at both ends from one of equal length that is open at only one end. For a pipe of length L open at both ends, the wavelength for the second harmonic (first overtone) is equal to L:

In contrast, for a pipe open at one end and closed at the other, the wavelength is equal to :

Keep in mind that the first overtone for a closed pipe corresponds to the third harmonic, not the second. Thus, when the brother covers one end of the flute, the wavelength increases. Given that the wavelength and the frequency of a sound are inversely proportional, an increase in wavelength corresponds to a decrease in frequency. Therefore, when the brother covers one end of the flute, the sound produced by the instrument will be slightly lower in pitch than the original sound.

Previous       Next