Some concepts for a Conceptual Physics class

1. Refraction
 Bending of a wave as it enters a new medium
This bending is caused by a
change in the wave’s velocity and
wavelength.
(The frequency does not change.)
Speed of Light?
c = 2.99792458 x 108
m/s (in a
vacuum)
Even light goes slower in a
medium. Why?
It takes longer for each atom to
absorb and reemit than to travel
through nothing.

2. Index of Refraction (n)
 ratio of the speed of light (c) in a vacuum to
the speed of light through the medium (v)
What would be the
speed of light traveling
through Plexiglas?
8
8
3 10
1.51
1.99 10 /
c
n
v
x
v
v x m s
=
=
=
Common Values of n
Vacuum 1
Air 1.0003
Water 1.33
Glass 1.46-1.58
Plexiglas 1.51
Diamond 2.42
c
n
v
=
Table of others on Holt: page 490

3. Snell’s Law – Willebrord Snell (Dutch, early 1700’s)
When a wave entering a medium slows down,
it will always bend towards the normal.
When a wave entering a medium speeds up,
it will always bend away from the normal,
and part of the wave will be reflected.
ni sin θi = nr sin θr
Normal
Air
Glass
θi
θr
θi > θr

4. Sample Problem
A light ray of wavelength 589 nm traveling through
air strikes a smooth, flat slab of crown glass at an
angle of 30.0° to the normal. Find the angle of
refraction, θr.
Givens:
θi = 30.0°
ni = 1.00
nr = 1.52
θr = ?
ni sin θi = nr sin θr
1.00 sin 30 = 1.52 sin θr
sin θr = (1.00 sin 30)/1.52
θr = sin-1
(0.329)
θr = 19.2°
Practice: Holt 493: Practice A 1-3, Section Review 1-3

5. Polarization
• The Picket Fence Effect:
Since light is an
Electromagnetic Wave it
can be filtered.

6. Complementary Colors
Two or more
Colors that
when
combined will
show gray or
black.

7. Complementary Colors
Two or more
Colors that
when
combined will
show gray or
black.