Overview
This lecture covers Newton's laws of reflection and refraction and applies them to prisms and lenses, explaining how light bends and images are formed.
Newton's Laws of Optics
- Newton's second axiom is the law of reflection: the angle of incidence equals the angle of reflection.
- Newton's fifth axiom is the law of refraction (Snell's law): relates the angles when light passes between different media.
- The amount a light ray bends depends on the materials it travels through.
Refraction Through a Prism
- A prism is a triangular piece of glass with polished sides and parallel ends.
- When light enters the prism, it bends according to the ratio of the sine of the angle of incidence to the sine of the angle of refraction (17:11 from air to glass).
- As light exits the prism, the ratio reverses (11:17 from glass to air) due to Newton's third axiom.
- The diagram shows that the perceived location of an object (like a candle) is determined by extrapolating the refracted light ray backward.
Light Bending Through Lenses
- Lenses can be convex (curved outwards), concave (curved inwards), or a combination.
- Light rays from an object bend at each lens surface and focus to form an image at specific points.
- For each surface, the ratio of the sines (17:11 for entering glass, 11:17 for exiting) dictates the bending.
- The focused image can be captured by a sheet of paper, forming a visible image of the object.
Key Terms & Definitions
- Angle of Incidence — The angle at which a ray of light strikes a surface.
- Angle of Reflection — The angle at which a ray bounces off a surface; equal to the angle of incidence.
- Refraction — The bending of light as it passes from one medium to another.
- Snell's Law — Formula relating the angles of incidence and refraction using the ratio of sines.
- Prism — A transparent object with flat, polished sides that refract light.
- Lens — A piece of glass or plastic shaped to bend and focus light.
Action Items / Next Steps
- Review figures 12.1, 12.2, and 12.3 on page 142 for visual understanding.
- Practice tracing refracted rays through prisms and lenses using the ratio of sines.