Chapter 14
14-1 Characteristics of Light
White light is actually light that can be separated into six elementary colors of the visible
spectrum: red, orange, yellow, green, blue, violet
(differences in frequency and wavelength account for the different colors)
The spectrum includes more than visible light.
-human eye doe not see all light waves
Ex – X-rays, microwaves, radio waves
All are types of electromagnetic waves
Electromagnetic waves vary depending on frequency and wavelength.
Electromagnetic waves are:
 Transverse waves
 Made up of electric and magnetic waves which are at right angles of each
other
 Is continuous, there is no real separation between the different waves
 Determined by the frequency and wavelength
o Ex – radio waves have longer wavelengths than other waves
All electromagnetic waves move at the speed of light.
2.99792458 X 108 m/s (in vaccum)
2.99709 X 108 m/s (in air) ((which is slower))
= 3.00 X 108 m/s
C=fλ
Speed of light = frequency x wavelength
Brightness decreases by the square of the distance from the source.
Why is it that the further away you are from the source, the less bright the light appears?
14-2 Flat Mirrors
Reflection – the turning back of an electromagnetic wave at the surface of a substance
- most substances absorb at least some incoming light & reflects the rest
- a good mirror reflects 90% of light
The texture of a surface affects how is reflects light.
Diffuse reflection – light reflected from rough, textures surface in many directions
Specular reflection – light reflected from smooth surface in same direction
Incoming & reflected angles are equal.
Angle of incidence – angle between an incoming light ans the normal line at the point of
contact.
Angle of reflection – angle formed by the normal line to a surface and the direction in
which a reflected light moves
How does a mirror work? (flat mirror)
-
image distance = object distance
Image size = object size
Right side image ≠ right side object --- right to left reversal
Virtual image – an image formed by light rays that only appear to intersect
14-3 Curved Mirror
Concave Mirror
- image distance ≠object distance
- image size ≠ object size
Both distance and size are determined by the curvature of the mirror or also called the
radius of curvature.
1/p +1/q = 1/f
1/object dist. + 1/image dist. = 1/focal length
Curvature causes magnification of the image.
o Image is smaller than object = the magnification is less than 1
o Image is greater than object = the magnification is greater than 1
Magnification is a unit less quantity.
M = h’ / h
Magnification = image height / object height = - (image distance / object distance)
Real = negative M and upside down (inverted) when in front of mirror
Virtual = positive M and up right when in back of mirror
Convex Mirror
- allow virtual images and image distance is always negative
- take objects in a large field of view and produce a small image
- image distance ≠object distance
- image size ≠ object size
14-4 Color
How does an object appear white?
How does an object appear green (or any other color)?
How does an object appear black?
Additive primary colors – red, green, blue - because they can produce all of the colors of
the spectrum in light
Additive primary colors produce white light when combined.
Complementary color – color produced by two additive primary colors
How do pixels work in order for us to see a picture?
How do humans see colors and other animals do not?
Subtractive (pigments) primary colors filter out all light when combined.
Example – red light + green light = yellow light
red pigment + green pigment = black pigment
Why?
Primary pigments are cyan (blue green), magenta (red blue), & yellow.
- any 2 pigments make either red, green, blue
- when the 3 primary pigments are mixed correctly all the colors are subtracted
from white light and black is made.
Primary Additives (mixing light)
Red
Green
Blue
Red + green = yellow
Red + blue = magenta
Green + blue = cyan
Red + green + blue = white
These are complementary colors.
Primary Subtractive (mixing pigments)
Cyan (blue green)
Magenta (red blue)
Yellow
Yellow + cyan = green
Yellow + magenta = red
Cyan + magenta = blue
Yellow + cyan + magenta = black
These are complementary colors.
Chapter 15
15-1 Refraction
Objects appear to be in different positions due to refraction.
Refraction – the bending of a wave disturbance as it passes at an angle from one medium
to another
When looking at an object in water, will it look closer or further away than it actually is?
Answer:
Reason:
When looking at an object out of water when you are in water, will it look closer or
further away than it actually is?
Answer:
Reason:
15-2 Thin Lenses
Eyeglasses
Cornea – acts like a lens that directs light rays toward the retina
Retina – light-sensitive area in back of the eye
Crystalline lens – small lens that also refracts light
Two Sight Problems:
1. Hyperopia - Farsighted
-
eye attempts to focus on an object but the image position is behind retina
distant objects are clear but near are blurry
need a converging lens
2. Mypoia – Nearsighted
-
eye attempts to focus on an object but the image position is in front of retina
distant objects are blurry but near are clear
need a divergent lens
See page 577 Fig 15-5
15-3 Optical Phenomena
Fiber optics can guide light over a long distance.
-very little light intensity is lost; any lost is due to reflection from the 2 ends and
absorption by fiber
Reflected light produces mirages.
- a mirage is a phenomenon of nature produces by refraction in the atmosphere
- a person will see 2 images, one normal and the other toward the ground that is inverted
This is due to the different densities of air at different heights. This double image, with
one inverted, makes it look like a reflection in water.
- also seen on roads
Light rays from blue sky above are refracted by the warm air next to dark, hot
road.
Rainbows are created by dispersion of light in water droplets.
- sunlight is spread into a spectrum upon entering a spherical raindrop then internally
reflected on the back side of the raindrop
- perceived color of each water droplet then depends on the angle of which that drop is
viewed