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

Options

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

Explanation

To solve the question, "When a sound wave goes from one medium to another, the quantity that remains unchanged is:", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Properties of Sound Waves**:
Sound waves have several properties, including frequency, wavelength, amplitude, and speed. Each of these properties can change when sound travels from one medium to another.

2. **Identify the Key Properties**:
- **Frequency (f)**: The number of oscillations per second.
- **Wavelength (λ)**: The distance between successive crests of the wave.
- **Amplitude (A)**: The height of the wave, related to its loudness.
- **Speed (v)**: The speed at which the sound wave travels, which depends on the medium.

3. **Analyze How These Properties Change**:
- **Frequency**: Remains constant when sound travels from one medium to another. This is because frequency is determined by the source of the sound and does not change with the medium.
- **Wavelength**: Changes when sound moves to a different medium, as it is related to the speed of sound in that medium.
- **Amplitude**: Can change depending on the medium and how much energy is lost or gained during transmission.
- **Speed**: Changes as sound travels through different media due to differences in density and elasticity.

4. **Conclusion**:
Since frequency is the only property that does not change when sound waves transition between different media, the answer to the question is **frequency**.

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

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