Refraction of Light
Section 2.4
Why does light Bend??
• Remember in earlier classes when
we shone the laser through the air
into the beaker of water, and how
the result was a bending of the
light.
• This bending resulted from the light
ray striking the boundary where two
different substances met.
• Interface: refers to the boundary of
two different substances coming
together (i.e. air, water)
Refraction
• Refraction: is the bending of light as it
travels from one material to another
material
• The light bends as a result of a change in
the speed of the light
• Think of this as switching from running on
pavement, to running on a sandy beach (your
not slower, just the surface your running on is
making you slower). Your textbook uses the
example of traveling through the hallway
• The same applies to the speed of light
• Certain substances are easier for light to pass
through than others
Why does Refraction Occur??
• Refraction occurs anytime light
strikes a medium of different
density at an angle
• Medium: The intervening substance
through which impressions are
conveyed to the senses
• Figure 2.20 p. 201 of your textbook
• Uses figure skaters
• The idea is that a few hit a rough patch of
ice causing them to slow down, the rest of
the line continues at the same speed,
which is what creates the bend
• The same can be applied to light, when
part of the beam slows down, the rest of
the ray continues, and the ray of light will
bend
Optical Density
• The optical density of a
medium is not the same as its
physical density.
• The physical density of a
material refers to the
mass/volume ratio
• The optical density of a
material relates to the sluggish
tendency of the atoms of a
material to maintain the
absorbed energy of an
electromagnetic wave
Material
Index of Refraction
Vacuum
1.0000
Air
1.0003
Ice
1.31
Water
1.333
Ethyl Alcohol
1.36
Plexiglas
1.51
Crown Glass
1.52
Light Flint Glass
1.58
Dense Flint Glass
1.66
Zircon
1.923
Diamond
2.417
Rutile
2.907
Gallium phosphide
3.50
<--lowest optical density
<--highest optical density
Refraction in Different Media
• We now know that light bends when it strikes a new medium at an angle
• The denser the medium, the more it slows down the rays of light, the greater
the refraction
• Increase in Density of medium (more dense) = Decrease in the Angle of Refraction (Freaky
Science Teacher)
• Decrease in Medium (less dense) = Increase in the refraction angle (Sarah Farts A lot)
• Density is the same = No Refraction
Rate these three in order of Optical
Density based on their angles of refraction