Snell's Law describes the relationship between the incident angle, transmitted angle, and which property of the two media?

• A. Densities of the Media
• B. Acoustic Impedance
• C. Wavelengths
• D. Velocities of Sound in the Media

Answer: (D)

Snell's Law for waves tells us that how a wave bends at a boundary depends on how fast it travels in each medium. The relationship is governed by the speeds of the wave in the two media: the ratio of the sine of the incident angle to the sine of the transmitted angle equals the speed in the first medium divided by the speed in the second. In other words, the property that controls the refraction angle is the velocities of sound in the media. If the second medium is faster, the transmitted wave bends away from the normal; if slower, it bends toward the normal. The other options don’t set the refraction angle directly: density affects impedance but not the angle itself; acoustic impedance is a combined factor (density times velocity) and isn’t the Snell relation; wavelengths change across the boundary because velocity changes, but Snell's law uses velocities, not wavelength.