By reducing the amplitude of a sound wave, its :

Options

A. pitch increases
B. loudness decreases
C. loudness increases
D. pitch decreases.

Explanation

To solve the question "By reducing the amplitude of a sound wave, its:", we need to analyze the relationship between amplitude, loudness, and pitch.

### Step-by-Step Solution:

1. **Understanding Amplitude**:
- Amplitude refers to the maximum displacement of particles in a medium from their rest position when a sound wave travels through it.

2. **Understanding Loudness**:
- Loudness is a perceptual response to the intensity of sound and is influenced by the amplitude of the sound wave.

3. **Relationship Between Amplitude and Loudness**:
- It is known that loudness is directly proportional to the amplitude of the sound wave. This means that as the amplitude increases, the loudness also increases, and conversely, as the amplitude decreases, the loudness decreases.

4. **Analyzing the Options**:
- Option A: Pitch increases - This is incorrect because pitch is related to frequency, not amplitude.
- Option B: Loudness decreases - This is correct because reducing the amplitude will lead to a decrease in loudness.
- Option C: Loudness increases - This is incorrect as reducing amplitude cannot increase loudness.
- Option D: Pitch increases - This is again incorrect for the same reason as option A.

5. **Conclusion**:
- Therefore, the correct answer is **Option B: Loudness decreases**.

### Final Answer:
By reducing the amplitude of a sound wave, its loudness decreases.

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