1. Question of the Day:
Which path should a lifeguard (L) take at a
beach if she wants to reach the swimmer (S) in the
least time? Assume she can run faster in sand than
she can swim in water. L
sand
water S

2. This is an application of Fermat’s
Principle of Least Time

3. from one medium into another
___________________is the _____________of a wave as it passes_____________________________________.
Refraction
bending
from one medium into another
transmitted
Ex: It is the ___________________ wave that is
__________________ .
refracted
wavefront
ray
____________ diagram:
____________ diagram:
medium 1
surface
medium 2
reflected
Note: The _________________ wave is not shown here.

4. Huygens
Ex. Refraction explained using _______________
wavefronts.
 Each point on the surface serves as a _____________
source for new ________________ in the second medium.
point
"wavelets"

6. When a light wave refracts, its ____________ does
not change. This means its __________________ does
not change. But the _______________ does change.
color
frequency
speed
In medium 2:
In medium 1:
v = fl
v = f l
changes = (same)
changes
If speed increases, l ___________________ .
If speed decreases, l ___________________ .
increases
decreases
This is true for ______________________ .
all waves

7. Top view of wheels on an axle:=
pavement = fast medium
for wheels
grass = slow medium
for wheels
This wheel
slows down
while other
wheel is still
moving fast

8. Refraction of light causes mirages.
sand acts
like a mirror

9. Water wave refraction:

10. Refraction only occurs when a wave:
1/______________________________, AND
2/ enters the new medium _____________
(at an angle_________________________.)
changes speed
obliquely
other than 00
incident ray
reflected
ray
normal
medium 1
boundary
medium 2
refracted
ray

11. The _______________ ray is not refracted if EITHER
there is:
transmitted
incident
_____________
no speed change
(n1 = n2) 1 2
transmitted
…OR if:
2. ____________
____________
q1 = 00
incident 1
not oblique 2
transmitted

12. The _____________ray will ___________ be in the
Important points:
The _____________ray will
___________ be in the
quadrant that is _______
_______________of the
boundary as the
incident ray.
reflected
always
incident
ray
normal
on the
same side 1
boundary 2
The ______________ ray will
____________be in the
quadrant that is __________
of the quadrant of the
incident ray.
refracted
No rays
_________
in this
quadrant!
always
opposite

13. Ex: A ray is shown incident on a boundary, shown by
a darker line. Give the quadrant of the reflected and the
refracted ray. A/ C/ II I II I
refracted
reflected
III IV
III IV
refracted
reflected B/ D/ II I
reflected II I
refracted
III IV
III IV
reflected
refracted

14. ________________tells exactly how much refraction occurs. Snell’s Law
angle of
incidence q1 n1 n2
n1sinq1 =
n2 sinq2 q2
medium 1
medium 2
angle of
refraction
Calculators must be in ______________mode,
and not in ___________ mode.
degrees
radians

16. Page 2: bottom
Which medium
refracts waves
the most?
diamond
Which medium
refracts waves
the least?
air

17. Ex 1: Find the angle of refraction, q2
incident
600
air
Lucite
n1sinq1 = n2 sinq2 q2
1.5 sinq2
1.00 sin600 =
1.00 (0.866)
= 1.5 sinq2
0.5774
= sinq2
sin-1(0.5774) = q2
350 = q2

18. Ex 2: Find the absolute index of refraction of the
second medium, n2
300
zircon
unknown
460
n1sinq1 = n2 sinq2
1.92 sin300 = n2 sin460
1.92 (0.500) = n2 ( )
1.92 (0.500) = n2
1.33 = n2
What medium is the unknown?

19. Page 2: bottom

20.  _________________ angle  bends__________________ 2 decreasing
>
If v1 ____ v2
(or n1 ____ n2):
< 1
Decreasing v:
 _________________ angle
 bends__________________ 2
decreasing
towards normal
initial
direction
If v1 ____ v2
(or n1 ___ n2):
<
> 1
Increasing v:
__________________angle
 bends___________________ 2
increasing
away from normal
initial
direction

21. Ex: In which medium is light faster?1 2 1 2 H. B. E. 1 2 1 2 I. C. F. 1 2 1 2

22. apparent sun
The atmosphere
true sun
is below
horizon
Earth
your horizon
The sun has already set when you see it setting!

23. Ex. Pools of water
apparent
depth
actual
depth i o
farther
Objects in pools are _______________ than they appear!