Which statement is true about the frequency of a sound wave?

Which statement is true about the frequency of a sound wave?

• A. The frequency is determined by the source only.
• B. The frequency is determined by the observer.
• C. The frequency is determined by the environment.
• D. The frequency is a property of the medium only.

Answer: (A)

Frequency is the rate at which the source vibrates, creating the sequence of compressions and rarefactions that make a sound. That rate is set by the source itself, so the intrinsic frequency is determined by how fast the source is oscillating. The observer’s motion or the environment don’t change that emitted rate. If you’re moving toward or away from the source, you may hear a different pitch due to the Doppler effect, but the actual frequency produced by the source remains the same. The environment can change how fast the wave travels and what its wavelength is (since speed and wavelength depend on the medium), but it doesn’t alter the source’s emission frequency. That’s why the statement that the frequency is determined by the source only is the best description.

Frequency is the rate at which the source vibrates, creating the sequence of compressions and rarefactions that make a sound. That rate is set by the source itself, so the intrinsic frequency is determined by how fast the source is oscillating. The observer’s motion or the environment don’t change that emitted rate. If you’re moving toward or away from the source, you may hear a different pitch due to the Doppler effect, but the actual frequency produced by the source remains the same. The environment can change how fast the wave travels and what its wavelength is (since speed and wavelength depend on the medium), but it doesn’t alter the source’s emission frequency. That’s why the statement that the frequency is determined by the source only is the best description.