Announcements

Homework for tomorrow…
(Ch. 23, CQ6, Probs. 16, 18, & 53)
23.4: 5.4 m
23.8: 42°
23.10: 35°
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Office hours…
MW 12:30-1:30 pm
TR 9-10 am
F 10-11 am

Tutorial Learning Center (TLC) hours:
M 8-1 pm, 3-6 pm,
TR 8-6 pm,
W 8-1 pm, 2-6 pm
F 8-2 pm
Chapter 23
Ray Optics
(Image Formation by Refraction &
Color and Dispersion)
Last time…

Snell’s Law is…

Critical Angle, θc, for Total
Internal Reflection…
23.4:
Image Formation by Refraction
Q: If you see a fish that appears to
be swimming close to the front of
an aquarium, but then look through
the side, you’ll find that the fish is
actually farther than you thought.
Why?
23.4:
Image Formation by Refraction
Q: If you see a fish that appears to
be swimming close to the front of
an aquarium, but then look through
the side, you’ll find that the fish is
actually farther than you thought.
Why?
A: Refraction of light at the
boundary!
23.4:
Image Formation by Refraction
What is the image distance, s’, in
terms of the object distance, s, as
measured from the boundary?
23.4:
Image Formation by Refraction
What is the image distance, s’, in
terms of the object distance, s, as
measured from the boundary?
Notice:
n2 is the index of refraction of the
material that the light ray is
transmitted into.
Quiz Question 1
A fish in an aquarium with flat sides looks out at a hungry cat.
To the fish, the distance to the cat appears to be
1.
2.
3.
less than the actual distance.
equal to the actual distance.
more than the actual distance.
i.e. 23.6
An air bubble in a window
A fish and a sailor look at each other through a 5.0 cm thick
glass porthole in a submarine. There happens to be an air
bubble right in the center of the glass.
How far behind the surface of the glass does the air bubble
appear to the fish? To the sailor?
23.5
Color and Dispersion

Color is a perception, NOT a
physical quantity!

A prism disperses white light
into various colors.

When a particular color of light
enters a prism, its color does
NOT change.
23.5
Color and Dispersion



Different colors are associated with light of different
wavelengths.
The longest wavelengths are perceived as red light;
the shortest as violet light.
What we perceive as white light is a mixture of all colors.
Dispersion…

…is the slight variation of index of refraction with wavelength.
Below is the dispersion curves of two common glasses.
Notice:
 n is larger when the wavelength is shorter.

Dispersion…

…is the slight variation of index of refraction with wavelength.
Below is the dispersion curves of two common glasses.
Notice:
 n is larger when the wavelength is shorter.

Q: Which color travels faster
(in the material)?
Dispersion…

…is the slight variation of index of refraction with wavelength.
Below is the dispersion curves of two common glasses.
Notice:
 n is larger when the wavelength is shorter.

Q: Which color travels faster
(in the material)?
Q: Which color refracts more?
Rainbows…

The basic cause of the rainbow is a combination of
refraction, reflection, and dispersion.
Rainbows…

A ray of red light reaching your eye comes from a drop
higher in the sky than a ray of violet light.

You have to look higher in the sky to see the red light than to see the
violet light.
Quiz Question 2
A narrow beam of white light is incident at an angle on a
piece of flint glass. As the light refracts into the glass,
1.
2.
3.
It forms a slightly diverging cone with
red rays on top, violet rays on bottom.
It forms a slightly diverging cone with
violet rays on top, red rays on bottom.
It remains a narrow beam of white
light because all the colors of white
were already traveling in the same
direction.
Colored Filters and Colored Objects



Green glass is green because it absorbs any light that is
“not green.”
If a green filter and a red filter are overlapped, no light
gets through.
The green filter transmits
only green light, which is
then absorbed by the red
filter because it is “not
red.”
Colored Filters and Colored Objects



The figure shows the absorption curve of chlorophyll,
which is essential for photosynthesis in green plants.
The chemical reactions of photosynthesis absorb red light
and blue/violet light from sunlight and puts it to use.
When you look at the green
leaves on a tree, you’re seeing
the light that was reflected.