REFRACTION OF LIGHT
LEARNING GOALS
• We are learning why light bends.
• We are learning to calculate the index of refraction.
REFRACTION
• the bending of light as it moves
from one medium to another.
• Medium examples – air, water, oil,
glass, etc.
• Reflection occurs when light bounces
off an object.
• Refraction occurs because light
bends.
REFRACTION
WHAT IS THE SPEED OF
LIGHT?
• Through air: 3.00 x 108 m/s
• Through water: 2.26 x 108 m/s
• i.e. light SLOWS down when moving through a
denser medium
DRAWING REFRACTED RAYS
• normal - line drawn at right angle to boundary
between two mediums at ray's entry point.
• angle of refraction - angle refracted light ray
makes with normal inside material.
DETERMINING REFRACTED
ANGLE
• use a measurement called refractive index.
• a substance with a high refracted index is
more dense and therefore light will travel
slower through it (bends more).
• Common refractive indexes (see p. 524 for
more examples) Material
Refractive
Air
Pure water
Olive oil
Glass
index
1.00
1.33
1.49
1.52
ANGLE OF REFRACTION RULES
1. If light enters a slower medium (more
dense), the refracted ray bends towards
the normal.
2. If light enters a faster medium (less dense),
the refracted ray bends away from the
normal.
SNELL’S LAW
• used to calculate the refractive index (n):
c sin i
n 
v sin R
Where:
c = 3.0 x 108 m/s
v = speed of light in medium
i = angle of incidence
R = angle of refraction
n = refractive index
THE PENCIL PICTURE
• Why does the pencil appear bent in the
water?
• As light travels from the water into the air, the
speed of light increases and the light therefore
bends away from the normal
• Our brain doesn’t interpret this “bending”
correctly so it projects the light rays
backwards, making it look like the spoon has
bent.
EXAMPLE #1
• What is the refractive index of material in which light
travels at 2.5 x 108 m/s?
EXAMPLE #2
• How quickly would light travel in a material with a
refractive index of 1.75?
LEARNING GOALS
• We are learning why light bends.
• We are learning to calculate the index of refraction.
HOMEWORK
• P519 #2-4
• P.525 #2,3,6-8