1. Why is the sky blue?
Why are clouds white?
Why are sunsets red?

2. Optics
______________is the study of light.
Light is a ____________________________________wave.
transverse electromagnetic
__________– _________________
- _________________
Doppler effect
Light can act like a…
wave
diffraction
interference
…or like a ______________called a____________ .
particle
photon
(Visible) light is ________________________ .
all that you can see

3. ROYGB(I)V e&m spectrum
The electromagnetic ( _____ ) ___________________:
spectrum
ROYGB(I)V
The only differences between the different radiations
are their _________________ and/or __________________ .
For this reason, the entire ______________________is
sometimes referred to simply as ___________________ .
frequencies
wavelengths
e&m spectrum
light

4. Ex. Compare sound and light waves
vibration
type
type of
propagation
amplitude
determines:
frequency
sound
light
longitudinal
mechanical
loudness
pitch
transverse
e&m
brightness
color
Ex: Light waves in a vacuum: C: A: B: D:
Which light wave is brighter and blue-er?
Which is dimmer and blue-er?
Which is brighter and redder?
Which is dimmer and redder? D A B C

5. Ex: Put in order from slowest to fastest in a vacuum:
x-rays, blue light, radio waves
________ e&m radiation (light) travels ________________
________________________: ___________________________.
All
at the same
speed in a vacuum
Ex. Find the wavelength of a red light wave.

7. Ex: Put in order from slowest to fastest in a vacuum:
x-rays, blue light, radio waves
________ e&m radiation (light) travels ________________
________________________: ___________________________.
All
at the same
3.00 x 108 m/s
speed in a vacuum
Ex. Find the wavelength of a red light wave.
v = fl
3.00 x 108 m/s = ( ??? ) l

8. Reference Tables, page 2, top:
The Electromagnetic Spectrum
Are these
frequencies
or wavelengths?
Choose f = 4.0 x 1014 Hz

9. Ex: Put in order from slowest to fastest in a vacuum:
x-rays, blue light, radio waves
________ e&m radiation (light) travels ________________
________________________: ___________________________.
All
at the same
3.00 x 108 m/s
speed in a vacuum
Ex. Find the wavelength of a red light wave.
v = fl
3.00 x 108 m/s = ( ??? ) l
3.00 x 108 m/s = l
(4.0 x 1014 Hz)
0.75 x 10-6 m = l
7.5 x m = l
 small  little diffraction, normally

10. Wavefronts propagating from a source
plane
wavefronts
Spherical
wavefronts

11. ________________: A wave in one medium is _____________
on a surface (__________________ ) and returns back
______________________________.
Reflection
incident
boundary
into the same medium
perfectly smooth
Ex. waves incident on a _________________________surface
reflected
wave
incident
wave
surface

12. Reflection can be understood using Huygens
wavefronts that spread out from each point on
the surface as the incident wave arrives:
reflected
wave
incident
wave
surface

13. anechoic chambers
a(n) = no
echoic = echo
- very little reflected
sound waves….
Why?
Each time the sound
wave is reflected, it
loses some energy.

14. wavefronts
For simplicity, this:
direction of motion of wave
…will be replaced by this:
a “ray”
the direction
The ray arrow only shows _______________________
of the wave.

15. qi = qr qi qr Using only rays: incident reflected ray ray
normal
incident
ray
reflected
ray qi qr
surface
qi = qr
incident angle reflected angle
This is called the ___________________________.
Law of Reflection
with respect to
The angle q is always measured _________________
_____________________ .
the normal.

16. In the Physics Reference Tables: page 5

17. Ex: What is the angle of reflection? Draw the reflected ray. 600
incident
reflected
600
600
300
surface
Ex: What is the angle of incidence?
Draw and label the incident ray.
100
surface
100
incident
reflected
100

18. How does reflection change a wave?
reflected:
vr, fr, lr
incident:
vi, fi, li
normal
surface
vi = vr
1. Same medium  _________________
2. Same color  ________________
3. Since _____ = v/f,  _____________.
As a result, the _______________ wave has the same
_______________________ as the incident wave.
fi = fr l
li = lr
reflected
v, f and l

19. The Law of Reflection is _____________true…
1. …for ______ waves:
__________ ___________
2. …and is ______________________ of the v, f or l of the incident wave. This means that all
different ________________ of light and
_______________ of sound obey the Law.
always
all
light
sound
earthquake
water
gravity
etc
Ex:
400
________ angle
for any ________
surface

20. Sound waves obey the same Law of Reflection as light.
How do they “aim” the sound in these concert halls?

21. The Law of Reflection is _____________true…
1. …for ______ waves:
__________ ___________
2. …and is ______________________ of the v, f or l of the incident wave. This means that all
different ________________ of light and
_______________ of sound obey the Law.
always
all
light
sound
earthquake
water
gravity
etc
independent
colors
pitches
Ex:
400
400
same
________ angle
for any ________
color
surface

22. Reflecting telescopes: All colors reflect at the same
angle and meet at the same focus:
white
light
curved
mirror
focus
white
light

23. Why are some surfaces good _______________?
mirrors
Why are some surfaces good _______________?
Types of reflection:
Regular, mirror, specular
_____________________________: from smooth, flat
surfaces
2. _____________: from rough surfaces
diffuse
________
Regular
Diffuse

24. The Law of Reflection is obeyed for_______________
and____________________________.
both regular
diffuse reflection.
Even though the ______________ are in different
directions, the incident and reflected _________________ .
normals
angles are equal

25. Identify regular and diffuse reflections.

26. for visible light, whose l is ~ 10-6 to 10-7 m
3 m Liquid Mirror Telescope (LMT). This unique telescope used a pool of mercury spun in a dish at 10 rpm to form the primary mirror. The main limitation of the telescope was that it could only point vertically. The LMT was used to optically measure the low Earth orbit (LEO) debris environment. The telescope was located in Cloudcroft, NM and was closed in 2001.
These must be smooth
for visible light, whose
l is ~ 10-6 to 10-7 m
The Hubble mirror.

27. Why
aren’t
these
telescopes
smooth?

28. Compare radio wavelengths to visible wavelengths:
l = m
l = m
To the radio
wavelengths,
the telescopes
"appear"
smooth.

29. Ex: Driving at night: oncoming traffic dry you road: oncoming wet
diffuse reflection
you
rough surface  more diffuse reflection
 some light scattered back you see road
 less scattered forward  less glare for oncoming
oncoming
traffic
wet
road:
smooth surface  less diffuse reflection
 less light scattered back you can’t see road
 more scattered forward  more glare
for oncoming traffic

30. Why is the sky blue?
Why are sunsets red?

31. Water drops and ice crystals of all
Why are clouds white?
Water drops and ice crystals of all
different sizes scatter (reflect) all
different wavelengths (frequencies)
of light.
Why are clouds black?
…because they’re dirty!©
- in shadow of upper clouds
- light cannot penetrate to them.
©SuzieSmithProductions

32. Why is the ocean greenish-blue?
1. It reflects the sky.
2. It reflect blue wavelengths
better than other colors.
3. It absorbs red wavelengths
better. Lobsters on the ocean
floor appear black because
little red light gets down there

33. Why are Uranus and Neptune green/blue?
Methane in their atmospheres
absorb orange/red, so the
reflected light is the complementary
color.

34. Reflection nebulae – young stars, surrounded
by dust that scatter the blue light in our direction.

35. Ex: Albedo = percentage of incident light that is
reflected back from a planet or moon.
What is the albedo of the Moon? In other words,
of all the sunlight incident on the Moon, what
percentage is reflected back?
Only 0.07 = 7% on average!
out of 100%
only 7% on
average is
reflected back

36. It seems very bright against a dark sky.

37. Its brightness is best compared when
1. an "almost full" moon is rising after sunset; or
2. a "just past full" moon is setting at sunrise:
white building