Question

As the sound propagates through a medium, its _________ changes.

• A. (a) velocity
• B. (b) wavelength
• C. (c) frequency
• D. (d) amplitude

Answer 1

The correct option is D

(d) amplitude

Step 1: Explanation for the Incorrect answer

(a) velocity

1. The speed of the sound can be changed when it travels from one medium to another.
2. But it is unchanged when the sound moves in one medium.
3. So the velocity of a sound wave is constant when sound propagates through one medium.

(b) wavelength

1. The wavelength of the wave does not change as the sound wave propagates through one medium.
2. The speed of propagation is constant in one particular medium.
3. From the equation of velocity of sound we have $v=f\lambda$
4. Here, the frequency of the wave depends on the source and that does not change as sound moves through a medium
5. Velocity is also constant, So the wavelength of the wave is also constant when sound waves move in one medium.

(c) Frequency

1. The frequency of a wave is defined as the number of waves produced in one second.
2. The frequency of the wave is constant for one particular wave.
3. The value of frequency is characterized by the source by which the wave is produced.
4. In this case, the frequency does not depend upon the medium it only depends on the material by which the wave is produced.
5. The value of frequency remains the same when the wave travels from one medium to another
6. So, when the sound travels from one medium to another frequency of the wave remains unchanged.

Step 2: Explanation for the correct answer

1. The amplitude of the sound wave decreases with distance from its source.
2. because the energy is spread over a larger area as it moves further.
3. So, the amplitude of the sound wave changes as it moves in a medium.

Hence,

Option ( d) is correct