Transcript Psc CH-17 Reflection

Chapter 17
Reflection &
Refraction
Reflection
•When light rays
bounce back off of a
medium boundary
Refraction
•The bending of light
rays when passing
from one medium to
another
Ray
•A straight line path
representing the
direction of a light
wave
Regular Reflection
•Reflection off of a
smooth surface which
results in reflected wave
that are parallel
Regular Reflection
•Produce good images
• Mirrors give regular
reflections
Diffuse Reflection
• Reflection off of a rough
surface which results in
reflected waves that are
not parallel
Diffuse Reflection
• Because light waves are
scattered all over the
place, no image can be
seen
Law of Reflection
•The angle of
reflection equals
the angle of
incident
Law of Reflection
a
b
b = a
Normal 
Optical Density
• How fast light passes
through a substance as
compared to the speed
of light in a vacuum.
Optical Density
•As optical density
increases, the speed
in which light passes
decreases
Index of Refraction (n)
•Ratio of the speed of
light in a vacuum to
the speed of light in a
material
Indices of Refraction
•Vacuum: n = 1.00
•Air: n = 1.0003
•Water: n = 1.33
•Ethanol: n = 1.36
Indices of Refraction
•Crown glass: n = 1.52
•Quartz: n = 1.54
•Flint glass: n = 1.61
•Diamond: n = 2.42
Speed of Light in
Other Substances
nsub =
c
vsub
Speed of Light in
Other Substances
vsub =
c
nsub
Solve for the speed of
light in each of the
following:
water (n = 1.33)
crown glass (n = 1.52)
diamond (n = 2.42)
Solve for the speed
of light in a
substance with an
optical density of
1.50:
Snell’s Law
•The ratio of the sine of
the angle of incidence
over the sine of the angle
of refraction is constant
for any substance
Snell’s Law
n =
sin ai
sin ar
Snell’s Law
ni sin ai = nr sin ar
Snell’s Law
ai
n1 = air
ar
n2 = water
Draw a model with a
light ray passing from
one medium to another
more optically dense
medium. Include
reflection & refraction
A light ray from air
(nair = 1.00) & strikes
glass (nglass = 1.52) with
an incident angle of
o
30.0 . Calculate the
angle of refraction:
A light ray from air
(nair = 1.00) strikes glass
(nglass = 1.61) with an
o
incident angle of 36.9 .
Calculate the angle of
refraction:
A light ray from air
(nair = 1.00) & strikes
diamond (ndiamd = 2.42)
with an incident angle
o
of 45.0 . Calculate the
angle of refraction:
A light ray incident
from air (nair = 1.00) at
o
45.0 passes into an
unknown substance at
o
30.0 . Calculate its
index of refraction:
Total Internal Reflection
• When light passes from a
more optically dense
substance to a less optically
dense one, the angle of
refraction > the angle of
incident
b
a
Total Internal
Reflection (TIR)
•When the angle of
o
refraction  90 , total
internal reflection
occurs.
Calculate the angles where
TIR occurs when light passes
from the following to air:
water (n = 1.33)
crown glass (n = 1.52)
diamond (n = 2.42)
Applications & Effects
• Prisms
• Fiber Optics
• Mirages
• Red Sunsets
• Rainbows
Prisms
• When light pass through a
prism the various
wavelengths of light are
dispersed or separated into a
spectrum
Prisms
Fiber Optics
• A light wave can pass through a
thin glass thread surrounded by a
reflective substance. Even if the
glass thread is bent, the wave
passes through as it reflects off
the sides.
Mirages
•Light refracted
from a far away
source looks closer
Mirages
Sunsets & Rises
• Sunlight is refracted as it
strikes the atmosphere at
great angles bending light
towards Earth
Sunsets
• Because different
wavelengths are refracted
differently, colors change
Sunsets
Rainbows
• Sunlight is refracted &
reflected by rain droplets
dispersing the light into a
spectrum
Rainbows
Rainbows
Rainbows fall
o
from 40 – 42
from incident
Rainbows
Rainbows fall
o
from 40 – 42
from incident
A light ray from water
(nw = 1.33) & strikes
diamond (ndiamd = 2.42)
with an incident angle
o
of 53.0 . Calculate the
angle of refraction:
Answer the
questions at the
end of Chapter 16
Answer the
questions at the
end of Chapter 17
A light ray from water
(nw = 1.33) & strikes
glass (nglass = 1.51) with
an incident angle of
o
53.0 . Calculate the
angle of refraction:
Calculate the angle of
total internal
reflection of pukon
with n = 3.00
An incident ray from
air strikes quartz (n =
1.50) at an angle of
o
30 from normal.
Calculate: refl & refr