Refraction
Definition: Refraction
• Refraction is the movement of light from one
medium into another medium.
– Refraction causes a change in speed of light as it
moves from one medium to another.
– Refraction can cause bending of the light at the
interface between media.
To describe how much the speed of light is
affected by going from one medium to another,
we use index of refraction
Index of Refraction
• Refraction of light simulation
• http://www.thegms.org/msfiles/refraction/Lig
htRefract.html
• What happens when light hits the boundary
between two transparent mediums?
1) Part of the light is reflected – usually less than 5%
2) The rest is transmitted across the boundary
- The transmitted ray has a different direction than the
incident ray – it is refracted (bent at the boundary)
- If the transmitted ray travels from a medium with a higher
(n) value to a medium with a lower (n) value the refracted
ray will bend away from the normal
- If the transmitted ray travels from a medium with a lower
(n) value to a medium with a higher (n) value the
refracted ray will bend towards the normal
• When the index of
refraction decreases,
light bends away from
the normal.
n1 > n2
1
n1
2
When n1 > n2
1 < 2
n2
• When the index of
refraction increases, light
bends toward the
normal.
n1 < n2
1
When n1 < n2
1 > 2
n1
2
n2
Snell’s Law
n1 sinϴ1 = n2sinϴ2
Example: Snell’s Law
A search light on a yacht is being used at night to illuminate a
sunken chest. At what angle of incidence Θ1 should the light be
aimed?
Dispersion
• The separation of white light into colors due
to different refractive indices for different
wavelengths is called dispersion.
• Dispersion is often called the prism effect.
Dispersion
Which color of light has the greatest refractive index?
Critical Angle
Remember – when light passes from a medium
with a higher (n) to a lower (n), the light will
bend away from the normal
• This drawing reminds us
that when light refracts
from a medium with a
larger n into one with a
smaller n, it bends away
from the normal.
n1
n2
n1 > n2
If the angle of incidence increases so does the
angle of refraction
-
Critical angle is reached when the angle of
refraction = 90o
Critical Angle of Incidence
Ray reflects instead
of refracting.
c
• Instead of refraction,
total internal reflection
occurs when the angle
of incidence exceeds
the critical angle.
n1
r = 90o
n2
n1 > n2
Calculating Critical Angle
n1sin1 = n2sinϴ2
Example: Critical Angle
The drawing shows a ray of light whose angle of incidence is Θ1= 68.3o,
traveling through two solid materials and then undergoing total internal
reflection at a solid-liquid interface. What is the largest possible index of
refraction for the liquid?