The ______ states that the sum of the percent of sound reflected and the percent of sound transmitted must equal 100%.

• A. Law of refraction
• B. Law of attenuation
• C. Principle of superposition
• D. Law of conservation of energy

Answer: (D)

At an interface between two media, energy is redistributed rather than created or destroyed. A sound wave that hits the boundary splits into part that is reflected back and part that is transmitted into the second medium. If no energy is lost to absorption, the total incident energy equals the sum of the reflected and transmitted energies, so their percentages add up to 100%. In real materials some energy can be absorbed (turned into heat), which means the sum of reflected and transmitted can be less than 100%. The idea is a direct application of energy conservation. The other options describe how waves behave in different ways (direction change at boundaries, loss of amplitude with distance, or the principle of adding waves) but not the energy balance at an interface.