image of Eye on retina

D. Index of Refraction (n) – a comparison of speed of light in a substance to its speed in a vacuum

If a substance has an index of refraction of 2.00 it means light is twice as fast in a vacuum than it is in that medium

n = c/v

c = speed of light in a vacuum
(3.00 x 10⁸ m/s)

v = speed of light in a medium

n_vacuum = 1.00

n_air ≈ 1.00 , v ≈ 3 x 10⁸ m/s

Which substance slows down light the most when light enters from air?

Diamond,

(highest (n) index of refraction)

least?

Water

(smallest (n) index of refraction)

Any device with a lens refracts light

Ex 1) Speed of light in alcohol?

n = 1.36 (Reference Table)

n = 1.36 = c/v

1.36 = (3.00 x 10⁸ m/s)/V

3.00 x 10⁸ m/s = 1.36V

V = 2.21 x 10⁸ m/s

Magnifying glasses enlarge objects with refraction

n & v relationship?

n = c/v

Inverse

The more light is
slowed down

or sped up,

the more
it changes direction

Refraction in Glass

The human eye refracts light

1. Prediction θ_ref from θ_in

a. Snell's Law

n₁sinθ₁ = n₂sinθ₂

1 – incident medium

2 – refractive medium

Air/Lucite

n₁sinθ₁ = n₂sinθ₂

1.00 sin53 = (1.50) sinθ₂

.798 = 1.50sinθ₂

.798/1.50 = sinθ₂

.532 = sinθ₂

(inverse sine .532)

θ₂ = 32⁰

Enrichment

NOVA (PBS) explains how refraction makes diamonds sparkle