When a sound wave goes from one medium to another, the quantity X remains unchanged. X is

Options

A. speed
B. wavelength
C. amplitude
D. frequency

Answer

To solve the question, we need to determine which quantity remains unchanged when a sound wave transitions from one medium to another. Let's analyze the options provided: speed, wavelength, amplitude, and frequency.

### Step-by-Step Solution:

1. **Understanding the Transition of Sound Waves**:
- When a sound wave travels from one medium to another (for example, from air to water), various properties of the wave can change due to the differing characteristics of the media.

2. **Analyzing Speed**:
- The speed of sound is dependent on the medium through which it travels. In general, sound travels faster in denser media. Therefore, when sound moves from air (less dense) to water (more dense), its speed increases.
- **Conclusion**: Speed does change.

3. **Analyzing Wavelength**:
- The wavelength of a sound wave is related to its speed and frequency by the equation:
\[ v = f \lambda \]
where \( v \) is the speed, \( f \) is the frequency, and \( \lambda \) is the wavelength. If the speed changes while frequency remains constant, the wavelength must also change.
- **Conclusion**: Wavelength does change.

4. **Analyzing Amplitude**:
- The amplitude of a sound wave can also change when it moves from one medium to another due to various factors like energy loss and medium characteristics.
- **Conclusion**: Amplitude does change.

5. **Analyzing Frequency**:
- Frequency is determined by the source of the sound and does not depend on the medium. When sound travels from one medium to another, the frequency remains constant.
- **Conclusion**: Frequency does not change.

### Final Answer:
The quantity that remains unchanged when a sound wave goes from one medium to another is **Frequency**.