Refraction:
The “bending”
Refraction or
direction change
of light
Refraction in action…
Refraction
Water is acting like a lens, flipping the image.
• The Refraction of Light
most often occurs as light Refraction:
moves from one medium
or material, to another, The bending of
such as moving from air
into water. The water is light.
more optically dense than
the air – this means that in
the water, the light actually
travels slightly
slower. This ‘drag’ on the
speed of the light causes
the path of the light to
bend as it moves from the
air to the water. (Does not
bend when 90 degrees to
medium surface)
• Here we can see both
reflection and
refraction occurring at
a medium boundary.
• When light goes from
a less optically dense
medium to a more
dense medium it
bends toward the
normal (top). If it goes
from more dense to
less it bends away
from the normal
(bottom).
Where do you see refracted
images?
More effects…
Let’s examine the situation
in a desert where
mysterious pools of water
Mirage
appear for the thirsty
travelers. The light is
coming down to the
Earth’s surface at a severe
angle is actually bent by
the different layers of air,
curving upwards to arrive
at our eyes. When this
light arrives at our eyes,
we see the bright blue sky,
but this blue area appears
on the surface of the
Earth. This gives the
illusion of light bouncing off
water on the surface of the
sand.
How can you see the sun after it sets?
Total internal reflection
• There is a specific
angle at which light
will not refract
through at a medium
boundary but will
reflect instead. This
specific angle is
called the critical
angle.
• http://www.learnerstv.com/animation/
animation.php?ani=102&cat=physics
Total internal reflection
• The index of refraction is a value (ratio) Index of
which represents how much slower light
travels in a medium compared to light
traveling through a vacuum (or air). refraction
• The index of refraction, n, of other
transparent materials is defined through
the equation:………………………………
c
• where c is the speed of light(3x108m/s),
and v is the velocity of light in that
material.
n
• Because the refractive index of a vacuum
is defined as 1.0 and a vacuum is devoid
v
of any material, the refractive indices of all
transparent materials are therefore
greater than 1.0. For most practical
purposes, the refractive index of light
through air (1.0003) can be used to
calculate refractive indices of unknown
materials.
Some index values for various
mediums….
Material Refractive Index
Air 1.0003
Water 1.33
Glycerin 1.47
Immersion Oil 1.515
Glass 1.52
Flint Glass 1.66
Diamond 2.42
Zircon 1.92
• The angle of refracted light
is dependent upon both the
angle of incidence and the
composition of the material
into which it is entering.
• Light will pass into the
boundary at an angle to the
normal and will be refracted
according to Snell's Law:
• ni · sin(θi) = nr · sin(θr)
The Math
Putting it all together…
ni · sin(θi) = nr · sin(θr)
nr = vi = sin(θi)
ni vr sin(θr)
Where i = incident medium and r = refracted
medium.
http://www.animations.physics.unsw.edu.au/jw/light/Snells_law_and_refraction.htm
Different wavelengths of light
refract different amounts
Which color of light refracts most? It has the smallest wavelength.
How a rainbow is produced.
Different colors of light refract
different amounts….
Material Blue Yellow Red
(486.1 nm) (589.3 nm) (656.3 nm)
Crown Glass 1.524 1.517 1.515
Flint Glass 1.639 1.627 1.622
Water 1.337 1.333 1.331
Cargille Oil 1.530 1.520 1.516
Carbon Disulfide 1.652 1.628 1.618
Question
