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Refraction

When light passes from one material into another, it changes speed and bends. The refractive index n says how much slower light travels than in vacuum. When light enters a denser material, it bends towards the normal.

n_1\sin\theta_1 = n_2\sin\theta_2

Snell's law

n = \frac{c}{v}

refractive index

Symbols

$n$	refractive index
$\theta$	angle from the normal	°
$c$	speed of light in vacuum	m/s

Example

Light from air ( $n = 1$ ) into glass ( $n = 1.5$ ) at 30°:

$\sin\theta_2 = \sin 30^\circ/1.5 \approx 0.33$ , so $\theta_2 \approx 19^\circ$ .

Angles are always measured from the normal, not from the surface.

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