Early Work – Mar. 6
• List at least three places where you see or
use reflections.
Labs
• Light and Color
• Law of Reflection
• Law of Refractions
• Everyone turns in a lab
• 4 in a group
Early Work – Mar. 8
• What’s the difference between reflection
and refraction?
Lab
• In groups of four, with six mirrors, align the
mirrors at angles so that one object can
“see” another object.
– First put butcher paper on top of your desks
– After mirrors are aligned, mark mirror
placements (with chalk)
– Draw the line of sight between each mirror
– Measure the angles made with the normal
• Write a few sentences about what you
discovered doing this lab.
Ch 17
Reflection and Refraction
Demo
Law of Reflection
• Angle of Incidence
– The angle the incoming
beam makes with the
normal
• Angle of Reflection
– The angle the outgoing
beam makes with the
normal
Angle of Incidence = Angle of Reflection
Regular Reflection
• When parallel
rays hit a smooth
surface, such as a
mirror, they are
reflected in
parallel rays
Diffuse Reflection
• When parallel rays
hit a rough surface,
such as the page
of a book or a wall,
they are reflected
in all directions
Refraction
• A waves change in direction at
a boundary
• The beam in the first medium
is called the incident ray
• The beam in the second
medium is called the refracted
ray
• The angle of refraction is the
angle the refracted ray makes
with the normal
– If the angle of refraction is
smaller than the angle of
incidence, then the new medium
is more optically dense
Snell’s Law
• Willebrord Snell, in 1621, wrote
– The ratio of the sine of the angle of incidence
to the sine of the angle of refraction is a
constant (depending on the medium)
sin q i
n=
sin q r
Snell’s Law in General Cases
ni sin q i = nr sin q r
“n” found on P397 in book!
Example
• A light beam in air hits a sheet of crown
glass at an angle of 30.0°. At what angle
is it refracted?
Index of Refraction and the Speed
of Light
• The index of refraction is not only a
measure of how much the light will bend,
– But also of how fast light travels in the
medium
nsubstance =
c
vsubstance
Example
• Find the speed of light in water.
Early Work – Mar. 12
• A ray of light strikes a mirror at an angle of
incidence of 28°. What is the angle of
reflection?
• A ray of light has angle of incidence of
25.0° upon the surface of a piece of
quartz. What is the angle of refraction?
Total Internal Reflection
Critical Angle
occurs
when
a more is the
• The Only
critical
angle,
θCgoing
, of a from
substance
optically
dense
medium
intothe
a lesser
one
incident
angle
that
causes
refracted
(such the
as air)
ray to lie right along
boundary of the
To find θC, use Snell’s Law
substance.
Critical Angle
ni sin q i = nr sin q r
ni sin q i = nr sin 90
ni sin q i = nr
nr
sin q i =
ni
nr
q i = arcsin
ni
Effects of Refraction
• Mirages
• Lingering sunlight
• Shift of images in liquid
Rainbows
Bkwk
• P410: 1, 2, 3, 5, 6, 10, 11, 15, 16, 21, 22,
24, 31, 32, 33, 35, 36, 38, 39, 40, 44, 48,
49, 50, 51,
• Ch. 17 Quiz Wednesday!
– Must take prior to spring break