The pitch of an acoustic device can be increased by

Analysis

The question asks for the relationship between the pitch of a sound and other physical properties of a wave. In physics, pitch is a subjective quality of sound that allows us to classify it as "high" or "low."

Concept Explanation

• Pitch: This is the characteristic of sound that depends primarily on the frequency of the sound wave. A high-frequency sound wave is perceived as having a high pitch (like a whistle), while a low-frequency sound wave is perceived as having a low pitch (like a drum).
• Loudness/Intensity: These terms are related to the amplitude of the sound wave. Increasing the intensity or loudness makes the sound "louder" or "softer," but it does not change the pitch.
• Relationship: There is a direct proportionality between pitch and frequency. If you increase the frequency of a vibration, the pitch of the resulting sound increases.

Step-by-Step Solution

1. Evaluate Option A & B: These relate to loudness and intensity. Changing these affects how much energy the wave carries (amplitude), not how fast the wave oscillates (frequency). Therefore, they do not affect pitch.
2. Evaluate Option C: Pitch is defined by the number of vibrations per second (frequency). By increasing the frequency, you increase the number of cycles per second, which directly results in a higher pitch.
3. Evaluate Option D: Similar to A and B, decreasing intensity affects the volume of the sound, not the pitch.

Conclusion

Since pitch is directly dependent on frequency, increasing the frequency is the only way to increase the pitch of an acoustic device.

Exam Tip: Remember the mnemonic "Pitch = Frequency". If you are ever confused, think of a guitar string: tightening the string (increasing tension) makes it vibrate faster (higher frequency), which produces a higher note (higher pitch).