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 x10 8 m/s (in a vacuum). What is wavelength for 100,700,000 Hz FM radio wave?

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 Colors RED + GREEN =YELLOW RED+ BLUE = MAGENTA GREEN + 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