Total Internal Reflection
Critical angle, trapped light, fiber optics, and the sparkle of diamonds
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Check Your Understanding
5 quick questions — pick an answer to see if you’re right.
1. What is the critical angle?
2. A material bordering air has an index of refraction of 2.00. What is its critical angle?
3. Lucite's critical angle is 41.8°. Light inside Lucite hits the Lucite–air boundary at 50° from the normal. What happens?
4. Total internal reflection can occur only when light travels
5. Fiber optic cables carry light long distances through bends. What keeps the light inside the fiber?
Light in an Optical Fiber
Internet data travels as pulses of light through glass optical fibers. The light stays inside the fiber because of total internal reflection at the boundary between the glass core (n = 1.52) and its surroundings.
Under which conditions does total internal reflection occur?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
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C1. In a real fiber, the glass core (n = 1.52) is surrounded by glass cladding with n = 1.46. Substitute numerical values into a mathematical representation that can be used to determine the critical angle at the core–cladding boundary. Then calculate the critical angle.
C2. A ray inside the glass hits the glass–air surface at 30.° from the normal. What happens?
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response using a mathematical relationship.
C4. Determine the minimum time for a light pulse to travel through 1.0 km of the glass core (n = 1.52), assuming it travels straight along the fiber.
C5. Engineers surround the glass core with a layer of glass with a slightly lower index (the cladding). Why?
C6. Installers know that if an optical fiber is bent too sharply, the signal becomes weak. Explain why a sharp bend causes light to escape from the core.