LIGHT 1 Electromagnetic Energy EM Energy characteristics Radiant

LIGHT 1

Electromagnetic Energy • EM Energy characteristics: • • • Radiant energy Transverse waves Can travel through empty space Speed(c) = 3 x 108 m/s Made by vibrating an electron Faster than the Speed of Light? ? ? 2

EM Wavelengths • Light wavelengths are small - measured in “nm”; • Metric prefix – “n” = ? ? • But… λ must be in “meters” to use v = fλ • Ex: Violet light has a wavelength of 400 nm. How many meters is this? What is the frequency of violet light? • 400 nm = 400 x 10 -9 m • v = fλ • 3 x 108 = (f)(400 x 10 -9) • f = 7. 5 x 1014 Hz 3

Electromagnetic Spectrum Radioactive Martians Invade Venus Using X-ray Guns Visible: 750 to 400 nm Low frequency = long λ = low energy High frequency = short λ = high energy

Electromagnetic Spectrum Increasing Energy Increasing Frequency 400 700 5

Not all light is visible! • RMIVUXG • Red Martians Invaded Venus Using X-ray Guns Increasing Energy Increasing Frequency 6

BEHAVIORS OF LIGHT 7

Behaviors of Light • Light can behave in one of two ways: • As a WAVE • Five wave behaviors • As a PARTICLE • Two particle behaviors • Let’s explore the WAVE behaviors of light first…. . 8

WAVE Behaviors of Light • Five Wave Behaviors of Light 1. 2. 3. 4. 5. Reflection Refraction Diffraction Interference Polarization How do we see light? 9

Wave Behaviors of Light – 1. REFLECTION • Reflection – bouncing of light • Ex: Mirrors • Law of Reflection: • Θ i= Θ r • Angles measured in reference to a line that is perpendicular to the surface called the Normal 10

Wave Behaviors of Light – 1. REFLECTION • Law of Reflection Incident ray Reflected ray Normal Θi Θr Why is it dark at night? 11

Wave Behaviors of Light – 2. REFRACTION • Refraction – bending of light • Change in path due to change in speed • Change in speed caused by change in medium that light is traveling through • Ex: pencil in cup of water looks “bent” Air Water 12

Wave Behaviors of Light – 2. REFRACTION Snell’s Law: n 1 • sin θ 1 = n 2 • sin θ 2 13

Wave Behaviors of Light – 3. DIFFRACTION • Diffraction – spreading out of light • Diffraction grating disperses light into its component colors • Ex: hologram on credit card • colors seen on CD / DVD face 14

Wave Behaviors of Light – 3. DIFFRACTION 15

Wave Behaviors of Light – 4. INTERFERENCE • Interference – Constructive or destructive • Results in light/dark patterns • Ripple Tank The Original Double Slit Experiment 16

Wave Behaviors of Light – 4. INTERFERENCE 17

Wave Behaviors of Light – 4. INTERFERENCE 18

Wave Behaviors of Light – 4. INTERFERENCE 19

Wave Behaviors of Light 5. POLARIZATION • Polarization – light waves vibrating in one plane only • Light from sun is non-polarized • Polarizing filter lets only one vibration through, blocks all others • HEWITT image, p. 578 sunlight filter Only vertically vibrating light can get through If a second filter is placed on top of the first no light gets though 20

Behaviors of Light • Light can behave in one of two ways: • As a WAVE • Five wave behaviors • As a PARTICLE • Two particle behaviors • Now let’s look at the PARTICLE behaviors of light…. . 21

PARTICLE Behaviors of Light • Two Particle Behaviors of Light 1. Photoelectric Effect 2. Atomic Line Spectra 22

Particle Behaviors of Light – 1. PHOTOELECTRIC EFFECT • When light shines on a piece of metal, electricity flows • 1) Since electricity = flow of electrons, and 2)electrons are matter, 3) Waves don’t transfer matter, just energy! • You cannot use the wave behavior of light to explain this! • (? ) • Therefore, light must be made of particles called PHOTONS • Photon – a massless particle of light that has a specific amount of energy associated with it, depending on the frequency (color) of the light 23

Particle Behaviors of Light – 1. PHOTOELECTRIC EFFECT Phet Photoelectric effect 24

Particle Behaviors of Light – 2. ATOMIC LINE SPECTRA • Electron is hit by a photon • Absorbs the energy from the photon • Electron with more energy moves up to higher energy level • When electron “decays” back to lower energy level, it releases a photon • Released photons emit light – we see this light as specific colors • These energy level jumps are called quantum leaps • http: //phet. colorado. edu/simulations/sims. php? sim =Models_of_the_Hydrogen_Atom 25

The light at the end of the lecture…. . • LIGHT HAS A DUAL NATURE…. IT IS BOTH A WAVE AND A PARTICLE!!! 26

Now let’s talk about color… 27

Part I - Clays http: //www. omsi. info/visit/tech/colormix. cfm Color wheel • • Magenta + Cyan = Blue Cyan + Yellow = Green Yellow + Magenta = Red Magenta + Yellow + Cyan = Brown 2) Why isn’t the 3 -color combo black? 2) • Need to mix EXACTLY the same proportions of colors • What Cyan isare a little dark thetooprimary pigments? 2) • Magenta, Yellow, and Are Cyanthe primary pigments them to be? what you expected

Part II - Spotlights LED Color Combination Color you see Red + Green Yellow Green + Blue Cyan Blue + Red Magenta Red + Green + Blue White Light Color Wheel Pigment Color Wheel Red M W Blue C Y Magenta B R Blk Green Cyan G Yellow

Questions 1. What is the difference between light and pigments? 1. • light is color from rays, pigment is a dye in materials What are the primary colors of light? 1. • RGB – red, green, blue are the secondary colors of light? What • MYC – magenta, yellow, How cyan do the primary and secondary colors of light 1. • opposite How do you make white light? How do you make s 1. • combine equal parts RGB; remove How light do you make white pigment? How do you make 1. compare to the primary and secondary colors pigments? black light? black pigment? • remove pigments; combine equal parts MYC

Color • http: //micro. magnet. fsu. edu/primer/java/scienc eopticsu/newton/ • Isaac Newton was the first scientist to make a systematic study of color. By passing a beam of sunlight through a prism, he showed that the light could be separated into the colors of the spectrum: ROY G BIV • White is not a color - it is all the colors combined. • Black is not a color either - it is the absence of color.

Color By Reflection • The colors of most objects are due to the way that they reflect light. • Different materials and dyes absorb some colors of light and reflect others. The color that the object appears is the color of light that is reflected by the object. White light (RBG) Reflects R light Absorbs G&B light Flower absorbs B, Leaf absorbs R&B light White light (RGB) Flower reflects R&G light Leaf reflects G light

• What if you put the plant under magenta light instead? Flower absorbs B, Leaf absorbs R&B light Magenta light (B&R) Flower reflects Red light Leaf reflects nothing – black!

Three Color Theory • 3 types of nerves (cones) in the retina interpret the primary colors of light (Red, Green, and Blue. ) Our brains interpret the signals from these nerves to determine the “color” of an object. • Combining 2 primary colors of light will give a secondary color: • • Red + Green = Yellow Blue + Green = Cyan Red + Blue = Magenta Red + Blue + Green = White

Practice • What color does each of these objects appear? What do they White absorb? light White light Appears Y, absorbs B Red Green Appears M, absorbs G Red Blue You want a black room, but your mom doesn’t want to use three coats of primer to White get rid of it when you go to college. What light color light bulb can you use to make the cyan paint APPEAR black? Red Green Blue Appears C, absorbs R White Appears white, light absorbs nothing Green Blue Red

Practice • What color is produced by mixing the following colors of light? • Yellow + Blue = White • Magenta + Green = White • Cyan + Red = White

Complementary Colors • Whenever a primary color of light is mixed with its complementary secondary color, white light will be produced. • They are opposites on the color wheel • Combos are thought to “match” Primary color of light Complementary secondary color of light Green Magenta Red Cyan Blue Yellow

Pigments – Subtractive Color Formation • Pigments are colored materials that absorb certain colors and reflect others • They are present in dyes, paints, inks, etc. • Primary pigments absorb one color of light. Color of pigment Color of light absorbed Colors of light reflected Magenta Green Red Blue Cyan Red Blue Green Yellow Blue Red Green

Pigments – Subtractive Color Formation • Secondary pigments absorb two colors of light. Color of pigment Color of light absorbed Colors of light reflected Red Blue Green Blue Red Green Blue

Practice • What color would appear if the following pigments were mixed? • • Yellow + cyan = Green Cyan + magenta = Blue Magenta + yellow = Red Magenta + green = Black Cyan + red = Black Cyan + magenta + yellow = Black Whenever a primary pigment is mixed with its complementary secondary pigment, the color produced will be: Black

Check for understanding • • Why are the insides of binoculars and cameras painted black? • Black absorbs all color, so no light bounces off the sides of the lens and distorts the image. You put a piece of red cellophane over one flashlight and a piece of green cellophane over another. You shine the light beams on a white wall. What color will you see where the two beams overlap? • Yellow • You now put both the red and green cellophanes over one flashlight. If you shine the flashlight beam on a white wall, what color do you see? Explain. • Black. The white light goes through the red cellophane, which filters out G&B leaving only red light. Then the green cellophane filters out the red light, leaving no light to go through.