Ray Optics Cheat Sheet

Key Definitions

• Ray: A straight line representing the path of light.

• Optical Axis: A line perpendicular to the mirror or lens surface.

• Focal Point (F): The point where parallel rays converge or appear to diverge.

• Image: A reproduction of an object formed by rays of light.

Important Concepts

Reflection

• Law of Reflection: Angle of incidence equals angle of reflection (θi = θr) ✅

• Types of Mirrors:

• Concave: Converges light rays.

• Convex: Diverges light rays.

Refraction

• Snell's Law: n1 sin(θ1) = n2 sin(θ2) ✅

• Total Internal Reflection: Occurs when light travels from a denser to a rarer medium at an angle greater than the critical angle.

Lenses

• Convex Lens: Converges light rays.

• Concave Lens: Diverges light rays.

Key Formulas

• Mirror Formula: 1/f = 1/v + 1/u ✅

• f: Focal length

• v: Image distance

• u: Object distance

• Magnification (m): m = h'/h = -v/u ✅

• h': Image height

• h: Object height

Common Mistakes to Avoid

Common Mistake: Confusing the signs of distances in the mirror and lens formulae (use sign conventions carefully).

Memory Tricks

Tip: "FIRM" —

• F: Focal length

• I: Image distance

• R: Reflection

• M: Magnification

Key Diagrams

          Concave Mirror
               -----
              /     \
             /       \
            /         \
           /           \
          |     F     |
           \         /
            \       /
             \_____/
             
          Convex Lens
               -----
              /     \
             /       \
            /         \
           |     F     |
           |           |
           |           |
            \         /
             \_______/