Partial Refraction and Total
Internal Reflection
Snell’s Law

This is the relationship between the
angles of incidence and refraction. It
applies to refraction of light in any
situation regardless of the media
n1 sin 1  n2 sin  2
Review of Refraction
This is a great video that reviews the
concept of refraction we learned last
class. It also introduces the concepts of
partial refraction & total internal
refraction.
 You don’t need to know how to do
calculations with Snell’s Law, but know
that it can be used to predict the angle of
refraction.

Partial Refraction and Reflection


Occurs as light reaches a boundary between
two media
Some light is reflected and some is
refracted
Partial Reflection and Refraction

As the angle of incidence
increases more light will be
reflected and less refracted.
Rearview Mirror

During daytime driving,
the mirror is adjusted
so the light that hits
the mirror is directed
at the driver’s eyes.

At night, the driver
can flip a switch that
tilts the mirror,
reducing the amount
of light directed at
the driver’s eyes.
Total Internal Reflection
Total Internal Reflection

Critical Angle: angle of incidence that produces an
angle of refraction of 90 degrees

Total Internal Reflection (TIR):
occurs when the angle of incidence increases past the
critical angle.
can ONLY occur when light travels from a more
dense medium to a less dense medium
no longer any refraction and just reflection.
•
•
•
Total Internal Reflection
Total Internal Reflection
The critical angle
between glass and air
is less than 45.
 The prisms shown
change the direction of
the incoming ray of
light

◦ A: 90 degrees
◦ B: 180 degrees
◦ C: back in the same
direction
Applications of Total Internal
Reflection
Binoculars
 Retroreflectors

Applications – Optical Fibers
Contain a glass core
surrounded by
cladding made from
another type of glass
that has a lower
index of refraction.
 Such fibres achieve
total internal
reflection, which
allows data to be
transmitted.

Applications – Fibre Optics

Telecommunications
◦ signals are not affected by
electrical storms
◦ more signals can be
carried with less energy
loss
◦ the cables are smaller and
lighter

Medicine – Endoscopes
◦ One bundle carries light
into the required area,
while another bundle
carries an image of the
area back to a monitor.