Which term tells how much a ray will bend as it travels through its material?

• A. Angle of reflection
• B. Focal point
• C. Normal line
• D. Index of refraction

Answer: (D)

Light bends when it crosses from one material into another because its speed changes in different substances. The quantity that tells you how much bending will occur is the index of refraction. It is a property of the material that describes how much slower light travels there compared with vacuum, and it appears in Snell’s law, which governs the change in direction at the boundary. A larger difference between the surrounding medium’s index and the material’s index means a bigger bend; higher index means light slows more and bends toward the normal when entering that material. The angle of reflection describes bending due to reflection, not refraction; the normal line is just the reference line perpendicular to the boundary used to measure angles; the focal point relates to convergence or divergence by lenses, not the amount of bending inside a material. So the term that tells how much a ray will bend as it travels through its material is the index of refraction.