Chapter 19 Light

Objectives

• 19.1 Contrast EM waves with other kinds of waves

• 19.1 Describe the arrangement of EM waves on the EM spectrum

• 19.1 Explain at least one application of each type of EM wave

Objectives

• 19.2 Describe the differences among opaque, transparent, and translucent materials

• 19.2 Explain how you see color • 19.2 Describe the difference between light

color and pigment color

Objectives

• 19.3 Explain how incandescent and fluorescent bulbs work

• 19.3 Analyze the advantages and disadvantages of different light sources

• 19.4 State and give an example of the law of reflection • 19.4 Explain how refraction is used to separate white

light into the colors of the spectrum • 19.4 Describe how diffraction and interference

patterns demonstrate the wave behavior of light

Know Visible Light Order

Wavelength, Frequency, Speed of Light

• Same equation as before

• Where c = 3 x108 m/s (in a vacuum).

• What is wavelength for 100,700,000 Hz FM radio wave?

fc

Uses of Each type of EM spectrum

• Radio: Communication• Microwave: Cooking Food• Infrared: Night Vision• Visible: How you see the world• Ultraviolet: Tanning• X-Rays: Seeing bones, scanners at airport• Gamma Rays: Killing• Others?

Visible Light

• Composed of 7 regions– Red, Orange, Yellow, Green, Blue, Indigo, Violet• ROYGBIV

• Red is longest wavelength, lowest frequency, lowest energy

• Violet is shortest wavelength, highest frequency , highest energy

What you see

• If something is red, red light is reflecting off of the object back to you

• What is white? All the wavelengths of visible light hitting you – Don’t need all of them necessarily* Next slide

• What is black? None of the wavelengths of visible light is hitting you

Primary Addition Colors

• Red Light + Blue Light + Green Light = White Light

• What do we get when mix our primary colors together? Secondary colors– Red + Green = Yellow– Red + Blue = Magenta– Blue + Green = Cyan

Color• Color of material depends just as much on the

light that hits it as the material itself (if not more)

Primary ColorsRED + GREEN =YELLOWRED+ BLUE = MAGENTAGREEN + BLUE = CYAN

When red, blue, and green light are projected onto a screen, the overlapping areas appear different colors. Where all the three overlap, white is produced.

Additive primary colors are red, blue, and green because these colors produce the highest number of different colors.

• Complimentary colors are colors when added together produce white (just 2 colors).

• The complimentary colors are opposite of each other (Magenta + Green = White)

Questions

• The Paper is white under white light.

Color Subtraction

• Again, looking at an object, you see lots of frequencies of light hitting your eye.

• If a white light is shown onto the object, your eyes will see all the frequencies that reflect off the object, but not the ones absorbed.

• The ability of an object to absorb certain frequencies is color subtraction.

Color Subtraction

• The paper illuminated with white. The paper absorbs Blue, so Red and Green are reflected. Our eyes see this as Yellow.

• W - B = (R + G + B) - B = R + G = Y

Color subtraction also applies to the transmission of light

Pigments

• Pigments: Absorb Light. Pure pigments absorb only a single frequency, compound pigments will absorb multiple frequencies of light.

• A pure Blue pigment absorbs Yellow Light (Red and Green).

• A pure pigment absorbs its complimentary color.

Questions

• Magenta is what two colors?• Cyan is what two colors?• Yellow is what two colors?• A blue shirt is blue because it – A) Absorbs which colors– B) Reflects which colors– C) What does a blue shirt look like under yellow

light?

Painting

• How do you produce the following colors using Magenta, Cyan, and Yellow pigments?

• Red?• Blue?• Green?

Other light terms

• Opaque: Visible light doesn’t pass through– Like a wall

• Translucent: Visible light passes through, but image distorted– Frosted glass

• Transparent: Visible light passes through and you can see the image– A window

Reflection of Light

• Specular: Mirror • Diffuse: Everything else

Refraction

• Light bends when it changes mediums

• Light slows down in water, so that is why it bends

Where does the Bird see the Fish?

Going Fishing

• Light travels at slightly different speeds when you change temperature.

• Leads to refraction

Diffraction of Light

• Diffraction refers to bending of a wave around an object