Chapter V review: tests and summary
Light travels in vacuum at c = 299 792 458 m/s ≈ 3·10⁸ m/s; it was measured by Roemer (astronomical method) and Fizeau (c = 4lNν). Law of reflection: γ = α; law of refraction: sin α/sin β = n₂/n₁ = v₁/v₂, where n = c/v. In an optically denser medium the ray bends toward the perpendicular. In going from a dense to a rarer medium, if the angle of incidence exceeds that given by sin α₀ = n₂/n₁, the ray is totally reflected; this is used in fibre-optic cables and prismatic mirrors. For a lens D = 1/F, 1/F = 1/d + 1/f, Γ = f/d; for d > 2F the image is real, inverted and reduced, for d < F virtual, upright and enlarged. A magnifier has K = D₀/F (D₀ = 25 cm), a microscope K ≈ lD₀/(F₁F₂), a telescope K = F_obj/F_eye. Short-sightedness is corrected with concave (D < 0) and long-sightedness with convex (D > 0) spectacle lenses. Solar technology is used to get heat and electricity from solar energy.
Review map: draw three columns – “Light”, “Lens” and “Instruments and eye” – and write the main formulas, an everyday example and one problem in each. Quiz each other with a friend.