Overview
This lecture explains how light refracts when moving between materials of different densities, introduces the concept of refractive index, and provides the formula for calculating it.
Refraction Basics
- Refraction occurs when light changes direction as it moves between substances of different densities.
- The greater the difference in density between substances, the more the light bends (refracts).
- Light slows down and bends toward the normal when it enters a denser substance (e.g., air to glass).
- In a less dense substance, light speeds up and bends away from the normal.
Practical Tools and Memory Aids
- The acronym "FAST" helps remember: Faster Away, Slower Towards (the normal).
Refractive Index
- Every transparent material has a refractive index, which measures how much light slows down compared to its speed in a vacuum.
- The refractive index (n) is calculated as: n = sin(angle of incidence) / sin(angle of refraction).
- Example: For an incident angle of 65° and a refraction angle of 40°, n = 1.41.
- A higher refractive index means greater bending of light toward the normal.
Applications of Refractive Index
- Materials with higher refractive indices are useful for making powerful lenses without requiring thick glass.
Key Terms & Definitions
- Refraction — The change in direction of light when it passes between substances of different densities.
- Normal — An imaginary line perpendicular to the boundary at the point of incidence.
- Angle of incidence (i) — The angle between the incoming ray and the normal.
- Angle of refraction (r) — The angle between the refracted ray and the normal.
- Refractive index (n) — A measure of how much light slows down in a substance, calculated as n = sin i / sin r.
Action Items / Next Steps
- Practice using the refractive index formula with different angles.
- Review examples of lenses with different refractive indices.