Which statement about light entering a diamond at the maximum refraction angle is true?

Which statement about light entering a diamond at the maximum refraction angle is true?

• A. It Exits the Diamond at the Same Angle It Entered
• B. It Is Always Absorbed at the Surface
• C. It Has No Effect on Internal Reflection
• D. It Forms a Critical Angle Cone Inside the Diamond

Answer: (D)

Light entering from a less dense medium into a diamond must follow Snell’s law, so as the incoming ray becomes more grazing, the refracted ray inside the diamond can only bend up to a maximum angle relative to the normal. That maximum inside the diamond is the critical angle for the diamond–air boundary. At this angle, the ray inside travels just at the limit where it could exit the boundary, and if it reaches another surface, it would hit that surface at this critical angle. In three-dimensional space, all such internally guided rays with that angle to the normal form a cone around the normal—the critical angle cone. So, when light enters at the largest possible refracted angle, it sets up that cone of directions inside the diamond, which is why the statement about forming a critical angle cone is the true one.

Light entering from a less dense medium into a diamond must follow Snell’s law, so as the incoming ray becomes more grazing, the refracted ray inside the diamond can only bend up to a maximum angle relative to the normal. That maximum inside the diamond is the critical angle for the diamond–air boundary. At this angle, the ray inside travels just at the limit where it could exit the boundary, and if it reaches another surface, it would hit that surface at this critical angle. In three-dimensional space, all such internally guided rays with that angle to the normal form a cone around the normal—the critical angle cone. So, when light enters at the largest possible refracted angle, it sets up that cone of directions inside the diamond, which is why the statement about forming a critical angle cone is the true one.