Transcript Chapter 15

Refraction
Section 14-1
Refraction ~ the
bending of a wave as it
passes at an angle from
one medium into
another.
Refraction occurs
because of a change in
the wave speed.
 With light, if the
speed decreases
going from the first
to the second
material, the ray is
bent towards the
normal.
 If the speed
increases in the
second material,
the ray is bent away
from the normal.
The index of refraction, n, is the ratio of the speed of
light in a vacuum (c) to its speed in a given medium
(v).
c
n
v
The slower the speed, the more optically dense the
medium is and the greater n is.
Index of Refraction for Various
Substances:
Water at 20 degrees C
1.333
Ice at 0 degrees C
1.309
Air at 0 degrees C
1.000
CO2 at 0 degrees
1.000 450
Medium 1
Medium 2
Incident
Ray
i
Reflected
Ray
r
Refracted
Ray
The relationship between the angles of
incidence and refraction is given by
Snell’s Law
Snell’s Law
n1(sin 1) = n2(sin 2)
n1= index of refraction for medium 1
1 = incident angle
n2 = index of refraction for medium 2
2 = refracted angle
Section 14-1
Practice Problem
A light ray of wavelength 598 nm (produced by a sodium lamp)
traveling through air strikes a smooth, flat slab of crown glass at an
angle of 30.0 degrees to the normal. Find the angle of refraction,  r.
Given:
1 = 30 degrees
n1 = 1.00
n2 = 1.52
Unknown:
2 = ?
Use the equation for Snell’s Law:
Ni(sin i )= N r (sin  r )
 r = sin-1 [(ni / nr) (sin  i)] = sin=1 [ (1.00 / 1.52) (sin 30 degrees)]
 r = 19.2 degrees