Refraction
Chapter 15
Refraction
• Refraction: The bending of light as it
travels from one medium to another
• Refraction occurs when light’s velocity
changes
• The speed of light varies with the medium
Refraction
Θi = Angle of Incidence
Θr = Angle of Refraction
Index of Refraction
• Index of Refraction = speed of light in vacuum
speed of light in medium
n
c speed of light in a vaccuum

v speed of light in the medium
*Only valid for light with wavelength of 589 nm in a
vacuum (p. 564)
Snell’s Law
Snell’s Law determines the angle of
refraction
nisin(θi) = nrsin(θr)
ni = Index of refraction of first medium
nr = Index of refraction of second medium
θi = Angle of Incidence
θr = Angle of Refraction
Bending relative to the normal
• When light passes from a medium with a
low index of refraction to a medium with a
high index of refraction, the ray bends
toward the normal
• When light passes from a medium with a
high index of refraction to a medium with a
low index of refraction, the ray bends away
from the normal
CATBEAR trying to catch a
fish!!!
Sample Problem (p.567 #4)
• Sunlight passes into a raindrop at an angle
of 22.5° from the normal at one point on
the droplet. What is the angle of
refraction?
Sunlight into a raindrop
• Will the ray bend away from the normal or
towards the normal?
– Low n to high n, the ray will bend toward the
normal
θi
θr
Use Snell’s Law
ni sin  i  nr sin  r
ni sin  i
sin  r 
nr
1  ni sin  i
 r  sin 
 nr



(
1
)(sin(
22
.
5
)
1
  sin 
  16.68
1.333


