What happens to the angle of transmission if the speed of sound in the second medium is less than in the first when the sound beam hits at an angle?

• A. Increases
• B. Decreases
• C. Remains the same
• D. Becomes undefined

Answer: (B)

When a sound wave transitions from one medium to another at an angle, the relationship between the speeds of sound in the two media directly affects the angle of transmission. According to Snell's law, which describes how waves refract when entering a different medium, the angle of transmission will change depending on the relationship between the speeds in the two media.

If the speed of sound in the second medium is less than in the first, the sound wave will slow down upon entering the second medium. This slowdown results in the wave bending towards the normal line (the imaginary line perpendicular to the boundary between the two media). As a result, the angle of transmission decreases compared to the angle of incidence, which is the angle at which the wave approaches the interface.

This phenomenon is analogous to how light behaves when it moves between different optical media with varying refractive indices. Thus, the correct answer reflects the fact that a lower speed in the second medium than in the first leads to a smaller angle of transmission when the sound beam hits at an angle.