ACOUSTICS — Identify the unit for the specified quantity. Question: Which unit is commonly used to express the amplitude (level) of sound in practical measurements?

Introduction / Context:
In acoustics, several related but distinct quantities appear: pressure amplitude, intensity, and sound level. Everyday instruments (sound level meters) typically report levels in decibels (dB), a logarithmic measure referenced to a standard threshold. This question tests recognition of the practical unit used to report how “loud” a sound is.

Given Data / Assumptions:

• We focus on standard reporting of sound magnitude in practice.
• Decibel is a logarithmic ratio unit; coulomb is electric charge; “hum” is not a unit; “cycles” relates to frequency; pascal is pressure.

Concept / Approach:
Human hearing spans a vast dynamic range. Using a logarithmic scale (decibel) compresses this range into manageable numbers. While the underlying physical amplitude could be sound pressure in pascals, practical sound “amplitude” or level for environments, industry, and safety is expressed in dB SPL (sound pressure level), referenced to 20 μPa.

Step-by-Step Solution:
Recognize the real-world reporting convention: SPL in dB.Relate physical quantity: level relates to pressure amplitude via logarithmic formula.Eliminate unrelated electrical or non-units.Choose decibel as the standard practical unit.

Verification / Alternative check:
Noise regulations, workplace safety standards, and audio equipment specs all quote “85 dB,” “94 dB,” etc., confirming decibel as the everyday measure of sound magnitude.

Why Other Options Are Wrong:
B) Coulomb measures charge, not acoustics.C) “Hum” is a phenomenon, not a unit.D) “Cycles” label frequency counts; the SI form is hertz (Hz).E) Pascal is the base pressure unit; however, standard sound “amplitude” reporting is in decibel SPL.

Common Pitfalls:
Confusing raw pressure amplitude (Pa) with level reporting (dB). Exams usually expect “decibel” for practical sound amplitude/level.

Final Answer:
decibel