Lesson 5: Light & Optics

Light & Optics Reference

The Nature of Light

Light is an electromagnetic wave that also exhibits particle properties (photons). It travels at c = 3×10⁸ m/s in vacuum. The visible spectrum ranges from ~400 nm (violet) to ~700 nm (red).

Reflection

Law of reflection: angle of incidence = angle of reflection (both measured from the normal). Mirrors reflect light; specular reflection produces clear images; diffuse reflection scatters light in all directions.

Refraction & Snell's Law

When light passes from one medium to another, it bends. Snell's Law: n₁ sin θ₁ = n₂ sin θ₂. When light enters a denser medium (higher n), it bends toward the normal; less dense, away.

• Air: n ≈ 1.00
• Water: n ≈ 1.33
• Glass: n ≈ 1.50
• Diamond: n ≈ 2.42

Total Internal Reflection

When light in a denser medium hits the boundary at an angle greater than the critical angle, it reflects entirely back in. This is how fiber optics work.

Lenses

• Converging (convex) lens: bends parallel rays to a focal point. Used in magnifying glasses and cameras.
• Diverging (concave) lens: spreads rays apart. Used in eyeglasses for nearsightedness.
• Thin lens equation: 1/f = 1/dₒ + 1/dᵢ