Overview
This lecture covers the refraction of light waves, explaining how light changes direction at boundaries between different materials, and how to draw ray diagrams and understand triangular prisms.
Refraction of Light
- Refraction is the change in direction of a wave as it passes from one medium to another.
- Light travels at different speeds in different materials due to varying densities.
- In denser materials, light travels more slowly.
- When light moves from a less dense medium (air) to a more dense one (glass), it slows down and bends.
- If the light enters at an angle (not perpendicular), its direction changes at the boundary.
- Light bends towards the normal when entering a more dense medium, and away from the normal when entering a less dense one.
- The normal is an imaginary line perpendicular to the surface at the point of incidence.
Drawing Ray Diagrams
- Draw the normal at the point where the incident ray meets the surface.
- The incident ray is the incoming light ray.
- The refracted ray bends towards the normal if entering a more dense medium.
- Continue the refracted ray to the far side of the medium and draw a new normal.
- The emergent ray bends away from the normal when exiting to a less dense medium.
- Label the angle of incidence (between incident ray and normal) and angle of refraction (between refracted ray and normal).
Triangular Prisms and Dispersion
- White light contains all visible wavelengths.
- Different wavelengths bend by different amounts during refraction.
- Passing white light through a triangular prism spreads out the colors, forming a spectrum (rainbow effect).
Key Terms & Definitions
- Refraction — the bending of a wave as it passes from one medium to another.
- Normal — an imaginary line perpendicular to the boundary at the point where the wave enters.
- Incident Ray — the incoming wave or ray striking a surface.
- Refracted Ray — the wave or ray that has bent after entering a new medium.
- Emergent Ray — the ray that exits a medium after refraction.
- Angle of Incidence — angle between the incident ray and the normal.
- Angle of Refraction — angle between the refracted ray and the normal.
- Dispersion — splitting of white light into a spectrum due to varying refraction of its wavelengths.
Action Items / Next Steps
- Practice drawing ray diagrams for refraction through a rectangular block and a triangular prism.
- Review the wave speed equation and understand how wavelength changes with speed during refraction.