Early Work

1
Early Work Feb. 20

• Explain the uses of light
• Definitions from Ch. 16

2
Test Back
3
Ch 16

• Light

4
Light

• Light is the range of frequencies of
  electromagnetic waves that stimulates the retina
  of the eye

5
Light

• Wavelength range
• 400 nm violet
• 700 nm red
• ROYGBIV
• Light travels in straight lines
• Which makes shadows possible

6
Light

• Light behaves like both a wave and a particle
• Use ray model to model the path of light (which
  thinks of it as a particle)

7
Speed of Light

• Ole Roemer (1644 1710)
• First to determine light travels at a measurable
  speed
• Calculated velocity based on distance and time
  (Ios orbit is 42.5 hours)
• c 299, 792, 458 m/s
• c 3 x 108 m/s

8
Practice Problems

• P 376 1, 4

9
Early Work Feb. 22

• Explain how Roemer first calculated the speed of
  light.
• Turn in vocab and PP 1, 4

10
Sources of Light

• A luminous body emits light waves
• The sun
• An illuminated body reflects light waves
• The moon

11
Luminous Flux

• Luminous Flux, P
• The rate at which visible light is emitted from a
  source
• Measured in lumens, lm
• A standard 100-watt light bulb emits 1750 lm

12
Illuminance

• Illuminance, E
• The rate at which light falls on a surface
• Something we can use more than luminous flux
• Measured in lumens per square meter, lm/m2
• Or lux, lx
• Since light is emitted radially, use 4pr2 to find
  the surface area of a sphere

13
Illuminance

• Two ways to increase illumination
• Get a brighter source increase luminous flux
• Move object closer
• Both represented with

14
Luminous Intensity

• Luminous Intensity
• The luminous flux that falls on 1 square meter of
  a sphere 1 meter in radius
• Measured in candela, cd
• SI unit for all light intensity

P
P


E
2
p
p
4
4
d
15
Example

• What is the illumination on your desktop if it is
  lighted by a 1750-lm lamp that is 2.50 m above
  your desk?

16
Practice Problems

• 6, 7, 9 11

17
16.2

• Light and Matter

18
Materials

• Transparent materials
• Light waves are transmitted without distortion
• Translucent materials
• Light waves are transmitted with distortion
• Opaque materials
• Transmit no light, or reflect all light

19
Color

• Isaac Newton, at 24, did experiments on what he
  called the spectrum after observing it from a
  prism
• Through it unevenness in the glass

20
Color by Addition

• White light can be formed from the correct
  combination of red, green, and blue lights
• Primary Colors red, green, and blue
• Used in TVs
• Secondary Colors purple (magenta), cyan, yellow
• Red and green ? yellow
• Red and blue ? magenta
• Blue and green ? cyan

21
Color by Addition

• If you have a color made by two other colors,
  then you already have two of the three colors
  needed to make white light.
• Complementary Colors a primary and a secondary
  that produce white light
• Magenta and green
• Yellow and blue
• Cyan and red

22
Colors by Subtraction

• Dye a molecule that absorbs certain wavelengths
  and transmits or reflects others
• Pigment a colored material that absorbs certain
  colors and transmits or reflects others
• Difference is a pigment is larger and can be seen
  with a microscope
• Often pigments are ground inorganic materials

23
Colors by Subtraction

• Primary Pigment absorbs one primary color
• Yellow absorbs blue and reflects red and green
• Cyan absorbs red and reflects blue and green
• Magenta absorbs green and reflects blue and red

24
Colors by Subtraction

• Secondary Pigment absorbs two primary colors
  and reflects one
• Red absorbs green and blue
• Green absorbs red and blue
• Blue absorbs red and green

25
Note

• Primary pigments are secondary lights
• Primary lights are secondary pigments

26
Mixing Pigments

• If the primary pigment yellow (which absorbs
  blue) is mixed with the secondary pigment blue
  (which absorbs everything but), then you get
  black because no wavelength is being reflected
• Remember, when you mix light you get white

27
Bkwk

• P 389 2 21, 24 44
• Hmwk due Wed. Feb. 28
• Ch. 16 Test Feb. 28