The transmission angle is defined as the angle between the transmitted wave and which line?

The transmission angle is defined as the angle between the transmitted wave and which line?

• A. The boundary surface
• B. The boundary's normal
• C. The incident ray
• D. The reflected ray

Answer: (B)

When a wave passes into a new medium, its path bends and we describe that bending using angles measured from the boundary’s normal—that is, the line perpendicular to the interface. The transmission (refraction) angle is specifically the angle formed between the transmitted wave and that normal line. Measuring from the normal keeps Snell’s law consistent, since n1 sin θi = n2 sin θt relates the incident and transmitted angles both to the same reference line. If you tried to measure from the boundary surface instead, you’d be using the complementary angle, which isn’t how refraction is defined. The incident angle is also defined from the normal, and the reflected ray is a separate case from the transmitted one.

When a wave passes into a new medium, its path bends and we describe that bending using angles measured from the boundary’s normal—that is, the line perpendicular to the interface. The transmission (refraction) angle is specifically the angle formed between the transmitted wave and that normal line. Measuring from the normal keeps Snell’s law consistent, since n1 sin θi = n2 sin θt relates the incident and transmitted angles both to the same reference line. If you tried to measure from the boundary surface instead, you’d be using the complementary angle, which isn’t how refraction is defined. The incident angle is also defined from the normal, and the reflected ray is a separate case from the transmitted one.