Sound _____ as it propagates.

Sound _____ as it propagates.

• A. Weakens
• B. Strengthens
• C. Remains constant
• D. Fluctuates

Answer: (A)

As sound travels through a medium, its energy spreads out and is absorbed, so it weakens. When a sound emanates from a source, the wavefront expands roughly like a sphere, so the same energy covers a larger area as distance increases. This geometric spreading causes the intensity to drop with distance (roughly proportional to 1/r^2), and the pressure amplitude decreases roughly in proportion to 1/r, so the sound becomes quieter as you move away. The medium itself also absorbs part of the energy, turning some of it into heat, and scattering can redirect energy away from the observer. Because of these effects, sound generally loses strength as it propagates. There can be special cases with amplification or interference that change local levels, but in ordinary propagation the trend is a weakening.

As sound travels through a medium, its energy spreads out and is absorbed, so it weakens. When a sound emanates from a source, the wavefront expands roughly like a sphere, so the same energy covers a larger area as distance increases. This geometric spreading causes the intensity to drop with distance (roughly proportional to 1/r^2), and the pressure amplitude decreases roughly in proportion to 1/r, so the sound becomes quieter as you move away. The medium itself also absorbs part of the energy, turning some of it into heat, and scattering can redirect energy away from the observer. Because of these effects, sound generally loses strength as it propagates. There can be special cases with amplification or interference that change local levels, but in ordinary propagation the trend is a weakening.