Which of the following factors does not affect the speed of sound?

Analyze the question: We need the factor that does NOT change how fast sound travels.

Concept: The speed of sound depends on the properties of the medium it travels through, not on properties of the sound wave itself, such as loudness (amplitude) or, in most cases, frequency.

For a gas, v = √(γRT/M), so speed depends on:

• Temperature: Higher temperature makes molecules move faster, so sound travels faster (about 331 m/s at 0°C, rising roughly 0.6 m/s per °C).
• Density and elasticity of the medium: In general, v = √(elastic modulus / density). Sound travels faster in solids than in liquids, and faster in liquids than in gases, mainly because of differences in elasticity.
• Wind (motion of the medium): If the air moves in the direction of the sound, the effective speed relative to the ground increases. If it moves against the sound, the effective speed decreases.

Check each option:

• A. Loudness: Loudness depends on amplitude (energy). A loud shout and a whisper travel at the same speed in the same air. It does not affect speed.
• B. Wind direction: It changes the effective speed of sound relative to the ground, so it affects speed.
• C. Temperature: It affects speed, as shown above.
• D. Material density: It affects speed, since v depends on density and elasticity of the medium.

Answer: The factor that does not affect the speed of sound is A. Loudness.

Exam tip: Remember that speed depends on the medium (temperature, density, elasticity, wind), not on the source or wave features (loudness, pitch or frequency). If a question asks which does not affect speed, look for loudness or amplitude.