Bell Work

1. Name your 5 senses.

2. What is required for you to see?

3. How does light travel?

4. Name two sources of light.

5. 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 )(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 of Light

• Illuminated source: reflects light waves

(Moon)

• Luminous source: emits light waves (Sun, light bulb)

Sources of Light

Light and Matter

Tran sp aren t Tran s lu cen t O p aq u e

Typ es o f M ate ria ls

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_optical_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

ColorNewton

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 blue and green makes cyan (light blue)

Adding all three makes white

again

Adding red and green makes

yellow

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 white hat would reflect all seven colours:

A pair of purple pants would reflect purple light (and red and blue, as purple is made up of red and blue):

Purple light

White

light

Using colored light

• If we look at a colored object in colored light we see something different. For example, consider the following:

White

light

Shorts look blue

Shirt looks red

• In different colours of light these clothes would look different:

Red

light

Shirt looks red

Shorts look black

Blue

light

Shirt looks black

Shorts look blue

Some further examples:

Object Color of lightColor object seems to be

Red socks

Red Red

Blue Black

Green Black

Blue teddy

Red Black

Blue

Green

Green camel

Red

Blue

Green

Magenta book

Red

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 area) red, yellow, green

b) Red, yellow, and blue

c) Red, green, and blue

d) Yellow, green, and blue

2. When red and green light shine on a white sheet, the resulting color isa) Blue

b) Cyan

c) Green

d) Yellow

e) Magenta

3. When red and blue light shine on a white sheet, the resulting color isa) Blue

b) Cyan

c) Green

d) Yellow

e) 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/index.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