Bell Work
1.
2.
3.
4.
5.
Name your 5 senses.
What is required for you to see?
How does light travel?
Name two sources of light.
What do you think is the difference
between translucent and transparent?
What is light?
• Light is energy traveling as an
electromagnetic wave
• Visible Light - the range of
frequencies of electromagnetic
waves that stimulates the retina of
the eye
Electromagnetic Spectrum
R
O
Y
G
B
I
V
Red Orange Yellow Green Blue Indigo Violet
(7 x 10-7 )
How does light travel?
• Light travels in straight lines
• We see this in shadows, flashlights
• The ray model of light shows that a narrow
beam of light travels in a straight line
• Light exhibits the same wave properties we
have studied: reflection, refraction,
diffraction
Sources of Light
• The sun is our primary source of
light
• Incandescent bulbs, florescent
bulbs, lasers, TV screens. LED
bulbs
Sources Sources
of Light
of Light
• Luminous
source: emits
light waves
(Sun, light
bulb)
• Illuminated
source: reflects
light waves
(Moon)
Light and Matter
Types of Materials
Transparent Translucent
Opaque
Transparent
• Materials that transmit light
waves
• Examples:
–air
–glass
–some plastics
Translucent
• Transmit light but do not permit
objects to be seen clearly
• Examples:
–lamp shades
–frosted glass
Opaque
• Transmit no light
• Absorb or reflect all light
waves
Measurements of light
• Eyes are sensitive to different
wavelengths
• Luminous flux (P)- rate that
light is emitted from a source
• Measured in LUMEN (lm)
Example: A 100 W bulb =
1750 lumen
Illuminance
• The rate at which light strikes a surface, E
• Think of this as the number of light rays
(the amount of light) that strikes a surface
• Measured in lux, lx
• Maximum sunlight- 100,000 lux
• Overcast day- 10,000 lux
Candela
• Candle power
• Measure of light
intensity
• Lumen –
measurement of light
intensity
• http://www.ted.com/talks/beau_lotto_optica
l_illusions_show_how_we_see.html
1. How does light travel?
2. Name two sources of light.
3. What is the difference between a translucent and
transparent object?
4. What is a standing wave?
5. What fraction of a wave is represented between the
antinodes of a standing wave?
6. What is the basic wave equation?
7. What units are wavelength and frequency measured in?
8. Name three types of electromagnetic radiation.
9. Convert 4.2 cm to meters.
10. Light travels at a speed of 3.0 x 108 m/s. Calculate the
frequency of light that has a wavelength of 5.8 x 10-7 m.
Electromagnetic Spectrum
• Light is energy emitted by accelerating electric
charges (photons)
• The energy travels in a wave that is both electric
and magnetic
• The range of waves, called electromagnetic waves,
can travel through a vacuum or matter
• When the light energy hits matter, the matter is
forced into vibration
Electromagnetic Spectrum
• All waves on the spectrum are the same in
nature
• Low frequency radio waves behave the
same as high frequency gamma rays
• The waves have different frequencies and
wavelengths
• All electromagnetic waves travel at the
same speed
Visible Light
• The lowest frequency of light we can see is
red light
• The highest frequency of light we can see is
violet light
• EM waves with frequencies lower than red
light are called infrared
• EM waves with frequencies higher than
violet light are called ultraviolet
Speed of Light
• Galileo was the first to try to measure the
speed of light
• He measured the time it took for light to
travel to a distant mirror and back
• Time was too short to measure
• Danish astronomer, Roemer made careful
measurements using the periods of Jupiter’s
moons
• Albert Michelson, an American physicist, is
credited with determining the speed of light
in an experiment using rotating mirrors and
a beam of light
Speed of Light
• The accepted speed of light is 3.0 x 108
m/s
• This universal constant is denoted with
the letter c
• The speed of light is found with the
same basic wave equation:
c=λf
Light Year
• A beam of light is so fast that it could travel
around the Earth 7.5 times in one second
• It takes about 8 minutes for light to travel
from the sun to the Earth
• The distance light travels in one year is
called a light-year
Color
Newton
determined that
white light was
made from a
combination of
color
The colors of the rainbow: ROYGBIV
• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet
Additive Color Mixing
• White light = RED LIGHT +
GREEN LIGHT + BLUE LIGHT
• These are considered Primary
Light Colors
• Yellow objects reflect yellow light,
absorbs all other colors
Adding colors
• White light can be split up to make separate colors. These
colors can be added together again.
• The primary colors of light are red, blue and green
Adding blue and red
makes magenta
(purple)
Adding red and
green makes
yellow
Adding blue and green
makes cyan (light blue)
Adding all three
makes white
again
Secondary Light Colors
• Formed by
mixing primary
colors
–Yellow
–Magenta
–Cyan
Complementary Colors
• Two colors that
add to produce
white light
–Cyan and Red
–Magenta and
green
–Yellow and blue
Seeing colour
• The color an object appears depends on the
colors of light it reflects.
For example, a red book only reflects red light:
White
light
Only red light is
reflected
A pair of purple pants would reflect purple light (and red and
blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light
Using colored light
• If we look at a colored object in colored
light we see something different. For
example, consider the following:
Shirt looks red
White
light
Shorts look blue
• In different colours of light these clothes
would look different:
Shirt looks red
Red
light
Shorts look black
Shirt looks black
Blue
light
Shorts look blue
Some further examples:
Object
Red socks
Blue teddy
Color of light
Color object
seems to be
Red
Red
Blue
Black
Green
Black
Red
Black
Blue
Green
Red
Green camel
Blue
Green
Red
Magenta book
Blue
Green
Using filters
• Filters can be used to “block” out different colors of light:
Red
Filter
Magenta
Filter
Concept Check
1. The three primary colors of light are
a)
b)
c)
d)
red, yellow, green
Red, yellow, and blue
Red, green, and blue
Yellow, green, and blue
2. When red and green light shine on a white
sheet, the resulting color is
a)
b)
c)
d)
e)
Blue
Cyan
Green
Yellow
Magenta
3. When red and blue light shine on a white
sheet, the resulting color is
a)
b)
c)
d)
e)
Blue
Cyan
Green
Yellow
Magenta
4. Complementary colors are two colors that
a) Look good together
b) Are primary colors
c) Are next to each other in the visible
spectrum
d) Produce white light when added together
5. The complementary color of blue is
a) Red
b) Cyan
c) Green
d) Yellow
e) Magenta
Color Blindness
• http://colorvisiontesting.com/ishihara.htm
Shadows
• A shadow is formed where light rays cannot
reach.
• A total shadow is called an umbra.
• A partial shadow is called a penumbra and
appears when some of the light is blocked,
but other light from another source fills in.
Making Color by Subtraction
• Objects can reflect and transmit light, and
they can also filter light.
• Colored filters transmit certain frequencies
of visible light while absorbing others.
• A blue filter absorbs red and green, a red
filter absorbs green and blue, and the green
filter absorbs red and blue.
Filters
• A filter can be used to block certain colors
of light
• Filters allow only certain frequencies to be
transmitted.
• http://www.michaelbach.de/ot/col_mix/inde
x.html
• A cyan filter absorbs red light, the magenta
filter absorbs green light, and the yellow
filter absorbs blue light.
Combining filters
• When a cyan (blue and green) and a yellow
(red and green) filter are mixed, the color
that results is green.
• When cyan and magenta filters are mixed,
blue results.
• When yellow and magenta are mixed, red
results.
Dye
• A dye is a molecule that absorbs certain
wavelengths of light and transmits or
reflects others.
• When white light falls on a red block the
dye molecules absorb blue and green, and
reflect the red light. The object appears red
to our eyes.
• See image on page 441 in text.
Primary Pigment
• Pigments are like dyes except they are made of
minerals.
• Primary pigments absorb only one primary color
of light. This means they reflect 2 colors of light.
• The primary colors of pigments are yellow, cyan
and magenta.
• A color printer uses the primary colors of paint to
produce any color imaginable.
Secondary Pigments
• A pigment that absorbs two colors of light
and reflects one is a secondary pigment.
• The secondary pigments are red, blue, and
green.
• The primary pigment colors are the
secondary light colors and the secondary
pigment colors are the primary light colors.
Complementary Pigments
• Red pigment is complementary to cyan.
• Blue pigment is complementary to yellow.
• Green pigment is complementary to
magenta.
• Complementary pigments are those that
when mixed, result in a black color.
6. The cyan color of ocean water is evidence
that the water absorbs __________light.
a. Red
b. Magenta
c. Yellow
d. Green
e. blue
7. When magenta and cyan light are mixed,
the resulting color is
a. blue
b. red
c. green
d. black
8. The mixing of cyan and yellow light to
produce the color green is an example of color
by
a. addition
b. subtraction
c. none of the above, this is not possible
9. A sheet of red paper will look black when
illuminated with ____light.
a. red
b. yellow
c. magenta
d. cyan
10. The color of an opaque object is
determined by the light that is
a. transmitted
b. absorbed
c. reflected
d. all of the above
11. What color will a yellow banana appear
when illuminated with blue light?
a. red
b. green
c. yellow
d. white
e. black
12. What color will a yellow banana look
when illuminated with green and red light?
a. yellow
b. blue
c. white
d. black
13. The primary pigments are
a. red, blue, and green
b. red, yellow, and green
c. cyan, magenta, and yellow
d. red, blue, and yellow
14. Complementary pigments are two
pigments that result in a _____color when
mixed.
a. white
b. black
c. brown
d. rainbow
15. The pigment complementary to magenta is
___.
a. red
b. blue
c. yellow
d. green
Polarization of light
• Non-polarized light (as in an incandescent
bulb) vibrates in all directions
• This means light waves are moving in
multiple directions at the same time.
• A single vibrating electron emits an
electromagnetic wave that is polarized.
• Polarized light oscillates in only one
direction.
Polarization
• A polarizing filter blocks light in one
direction.
• Light moving in a horizontal plane can be
blocked by a vertical filter.
• Light moving in a vertical plane can be
blocked by a horizontal filter.
Polarization by Reflection
• Light reflected off surfaces is partially
polarized.
• The light is polarized in the same plane as
the surface.
• Glare from a horizontal surface is
horizontally polarized.
• Which pair of
sunglasses is best
suited for
automobile drivers?
Pair C is best suited because
the vertical polarization axis
blocks horizontally polarized
light coming from the road.
Polarized Light and 3D Viewing
• Vision in three dimensions depends on the
fact that both eyes give impressions
simultaneously
• Each eye views a scene from a slightly
different angle
• The combination of views in the eye-brain
system give depth
3D Movies
• A movie can be seen in 3D when the left
eye sees the left view and the right eye sees
only the right view.
• This is accomplished by projecting a pair of
polarizing filters at right angles on the
screen.
• The overlapping pictures look blurry to the
naked eye.
• To see in 3D the viewer wears polarizing
glasses with the lens axes also at right
angles.
• Each eye sees a separate picture
• The brain interprets the two pictures as a
single image with a feeling of depth.
16. Light reflected from a lake surface is
polarized ______.
a. vertically
b. horizontally
c. randomly
17. In order for sunglasses to be effective in
reducing glare produced from a road, the
lasses should be polarized ____.
a. vertically
b. horizontally
c. both vertically and horizontally
18. Glasses used for 3D viewing are polarized
a. vertically
b. horizontally
c. both vertically and horizontally
19. If two polaroid filters are held with their
polarization axes at right angles to each other,
the amount of light transmitted compared to
when their axes are parallel is ___.
a. twice as much
b. the same
c. half as much
d. zero
20. Non-polarized light vibrates
a. vertically
b. horizontally
c. in all directions