1. L 32 Light and Optics [2] Measurements of the speed of light 
The bending of light – refraction 
Total internal reflection 
Dispersion
Rainbows
Atmospheric scattering
Blue sky and red sunsets
Mirrors and lenses n

2. The index of refraction (n) depends of the color (wavelength) of the light
Wavelength (nm) n
Red
660
1.520
orange
610
1.522
yellow
580
1.523
green
550
1.526
blue
470
1.531
violet
410
1.538
1 nm = m

3. Different colors are refracted (bent) by different amounts
White
light
red
contains all
wavelengths
(colors)
violet
Glass prism

4. The rainbow
Rainbows are caused by dispersion of sunlight from water droplets which act as tiny prisms

5. Why is it a rain BOW ? The drops must be At just the right
Angle (42 degrees)
Between your eyes
And the sun to see
The rainbow. This
Angle is maintained
Along the arc of a
Circle.

6. Atmospheric scattering
Why is the sky blue and sunsets red?
It is due to the way that sunlight is scattered by the atmosphere (N2 and O2)
Scattering atoms absorb light energy and re-emit it but not at the same wavelength
Sunlight contains a full range of wavelengths in the visible region

7. Atmospheric scattering: blue sky
Short wavelengths are scattered more than long wavelengths
Blue light (short) is scattered 10 times more than red light
The light that we see in the sky when not looking directly at the sun is scattered blue light

8. Atmospheric scattering: red sunset
At sunset, the sun is low on the horizon
When looking at the sun it appears red because much of the blue light is scattered out leaving only the red

9. Mirrors  reflection
Light does not pass thru metals – it is reflected at the surface
Two types of reflection: diffuse and specular
specular reflection:
Sharp image
Diffuse reflection:
Fuzzy or no image

10. The law of reflection The angle of reflection = angle of incidence
Incident ray, reflected ray and normal all lie in the same plane
Incident
ray
reflected
mirror
normal i r

11. image formation by plane mirrors
The rays appear to originate
from the image behind the
mirror. Of course, there is no
light behind the mirror  this
is called a virtual image
Mirrors appear
to make rooms
look larger.

12. You only need a mirror half as tall as you are to see your whole self
Homer’s image
Homer

13. The image of your right hand is your left hand
AMBULANCE is painted
backward so that you see
it correctly in your real-view mirror

14. Spherical or curved mirrors
Concave
mirror
Focus
parallel light rays are focused to one point

15. convex mirror focus parallel rays diverge from a focus behind
the mirror

16. Dish antennas signal from satellite detector at the focal
point of the dish

17. Magnifying mirrors Homer’s image Homer
when something placed within the focus of a concave
mirror, an enlarged, upright image is formed.
this principle is used in a shaving or makeup mirror

18. Convex mirrors: wide angle view
Object
Image
A convex lens provides a wide
angle view. Since it sees more,
the images are reduced in size.
Passenger side mirrors are often of this type with the warning: “objects appear further than they actually are". Because they appear smaller they look further away.

19. Image formation with lenses
converging lens (positive lens)
diverging lens (negative lens)
the human eye
correcting for nearsightedness
correcting for farsightedness
optical instruments
lenses are relatively simple optical devices
the principle behind the operation of a lens is refraction the bending of light as it passes from air into glass (or plastic)

20. converging lens a converging lens focuses parallel rays to
focal
point F
a converging lens focuses parallel rays to
a point called the focal point.
 a thicker lens has a shorter focal length

21. Diverging lens A diverging lens causes parallel rays to divergeF
A diverging lens causes
parallel rays to diverge
as if they came from a
focal point F

22. Image formation by a converging lens
object
If the object is located at a distance ofat least 2F from the
lens, the image is inverted and smaller than the object.
The image is called a REAL image since light rays
actually converge at the image location

23. A converging lens is used to focus rays from the sun to a point
since the sun is very
far from the lens, the
rays are nearly
parallel

24. converging lens is used in a camera to focus light onto the film
when you focus a camera,
you adjust the distance
between the lens and the
film depending on the
object location.

25. Image formation by a diverging lens
Object
image
The diverging lens produces an image that is upright
and diminished in size.
It is a VIRTUAL image, since light rays do not
actually pass through the image point

26. a magnifying lens Object virtual image
By placing the lens close to the object
we get a magnified virtual image.

27. Sight – the human eye Physics of the human eye
Corrections for abnormal vision
Nearsightedness
Farsightedness

28. The Eye light enters through the cornea
the iris controls the amount of light that gets in, a muscle can close it or open it, the iris is the colored part
the lens is filled with a jelly-like substance; the ciliary muscle can change the shape of the lens and thus change its focal length
by changing the focal
length, (accommodation) the lens
is able to focus light onto the
retina for objects located at
various distances

29. the physics of the human eye
The relaxed eye can easily focus on distant
objects. To focus on close objects the lens is squeezed to
shorten it’s focal length, making it possible to converge the
rays onto the retina. The near point is the distance at which
the closest object can be seen clearly. It recedes with age.

30. When a nearsighted person views a distant object, the lens
cannot relax enough to focus at the retina. The rays converge
too quickly. The remedy is to place a diverging lens in front
of the eye to first diverge the

31. When a farsighted person tries to focus on a close object
the lens cannot be squeezed enough to focus on the retina.
The focus point is behind the retina. The remedy is to place
a converging lens in front of the eye to converge the rays
before they enter the eye.
Weh

32. Pencil in lucite block
the top half of the pencil is glued exactly at the position where the image of the bottom half is formed in the block
due to refraction at the front surface the bottom of the pencil (its image ) appears closer to the front surface of the block
the bottom half of the pencil cannot be seen from the sides of the block because any ray from the bottom of the pencil suffers total internal reflection on the sides of the block.
top view