I. EM Radiation - Mrs. Ellis' Science Class! - Home

I. EM Radiation - Mrs. Ellis' Science Class! - Home

Ch. 15 Sound & Light I. Electromagnetic Waves & Radiation EM Waves EM Radiation EM Spectrum Types of EM Radiation LIGHT: What Is It? Light Energy

Atoms As atoms absorb energy, electrons jump out to a higher energy level. Electrons release light when falling down to the lower energy level. Photons - bundles/packets of energy released when the electrons fall. Light: Stream of Photons 2000 Microsoft Clip Gallery

Light What is it? Light can be modeled as a wave or as stream of particles or as rays that travel in straight lines Light What is it? Photons tiny, particle-like bundles of radiation absorbed and released by electrons

energy increases with wave frequency Speed of Sound Depends on medium type and medium temperature Speed in Vacuum 300,000,000 m/sec 186,000 mi/sec Speed in Other Materials

Slower in Air, Water, Glass Light travels much faster than sound. For example: 1) Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang.

A. EM Waves & Radiation Light waves are known as Electromagnetic Waves Consist of changing electric and magnetic field in space A. EM Waves & Radiation

Electromagnetic Radiation transverse waves produced by the motion of electrically charged particles does not require a medium Electromagnetic Spectrum 2000 Microsoft Clip Gallery

B. EM Spectrum The speed of light depends on the medium In a vacuum, light always travels at 3.0x108 m/s Travels faster in air than in water Fastest traveling signal in the universe B. EM Spectrum The brightness of light depends on intensity Intensity=the rate at which energy flows

through a given area of space As it spreads out, intensity decreases A 100W light bulb is brighter than a 60W light bulb B. EM Spectrum long short

low f high f low energy high energy

C. Types of EM Radiation Radiowaves lowest energy EM radiation Longest wavelength & Lowest frequency Uses: Radio & TV Broadcasting Modulating Radio Waves Modulation - variation of amplitude or frequency when waves are broadcast

AM amplitude modulation Carries audio for T.V. Broadcasts Longer wavelength so can bend around hills FM frequency modulation Carries video for T.V. Broadcasts C. Types of EM Radiation Microwaves penetrate food and vibrate

water & fat molecules to produce thermal energy C. Types of EM Radiation Infrared Radiation (IR) slightly lower energy than visible light can raise the thermal energy of objects Uses: cooking, medicine, TV,

Remote controls thermogram - image made by detecting IR radiation C. Types of EM Radiation Visible Light small part of the spectrum we can see ROY G. BIV colors in order

of increasing energy red R O Y G. orange

green yellow B blue I

indigo V violet Electromagnetic Spectrum Visible Spectrum Light we can see Roy G. Biv Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet.

Largest to Smallest Wavelength. C. Types of EM Radiation Ultraviolet Radiation (UV) slightly higher energy than visible light Types: UVA - tanning, wrinkles UVB - sunburn, cancer UVC - most harmful, sterilization

C. Types of EM Radiation Ultraviolet Radiation (UV) Ozone layer depletion = UV exposure! C. Types of EM Radiation X rays higher energy than UV can penetrate soft tissue, but

not bones Uses: medicine Lead absorbs X-Rays C. Types of EM Radiation Gamma rays highest energy EM radiation emitted by radioactive atoms

used to kill cancerous cells Radiation treatment using radioactive cobalt-60. Ch. 15 Sound & Light III. Wave Properties of Light Reflection Refraction

Diffraction Interference LIGHT: Particles or Waves? Wave Model of Light Explains most properties of light Particle Theory of Light Photoelectric Effect Photons of light produce free electrons

2000 Microsoft Clip Gallery A. Reflection Normal Reflection when a wave strikes an object and bounces off

incident beam reflected beam A. Reflection Law of Reflection the angle of incidence equals the angle of reflection

Part 2 - Reflection Reflection from a mirror: Normal Reflected ray Incident ray Angle of incidence

Mirror Angle of reflection LIGHT & ITS USES: Reflection Vocabulary Virtual Image Not Real because it cannot be

projected Image only seems to be there! Light & Its Uses: Mirrors Reflection Vocabulary Optical Axis Base line through the center of a mirror or lens Focal Point Point where reflected or refracted rays meet & image is formed Focal Length Distance between

center of mirror/lens and focal point 2000 Microsoft Clip Gallery LIGHT & ITS USES: Mirrors Plane Mirrors Perfectly flat Virtual Image is Not Real because it cannot be projected Erect Image is right side up

2000 Microsoft Clip Gallery LIGHT & ITS USES: Mirrors Reflection & Mirrors (Cont.) Convex Mirror Curves outward Enlarges images. Use: Rear view mirrors, store security

CAUTION! Objects are closer than they appear! 2000 Microsoft Clip Gallery LIGHT & ITS USES: Lenses Convex Lenses Thicker in the center than edges. Lens that converges (brings together) light rays. Forms real images and virtual images

depending on position of the object LIGHT & ITS USES: Lenses Object Focal Point Convex Lenses Ray Tracing

Lens Two rays usually define an image 2000 D. L. Power Ray #1: Light ray comes from top of object; travels parallel to optic axis; bends thru focal point. LIGHT & ITS USES: Lenses

Convex Lenses Ray Tracing Two rays define an image Ray #1 2000 D. L. Power Ray #2

Ray 2: Light ray comes from top of object & travels through center of lens. LIGHT & ITS USES: Lenses 2000 D. L. Power Concave Lenses Lens that is thicker at the edges and

thinner in the center. Diverges light rays All images are erect and reduced. How You See Near Sighted Eyeball is too long and image focuses in front of the retina

Far Sighted Eyeball is too short so image is focused behind the retina. 2000 Microsoft Clip Gallery 2000 Microsoft Clip Gallery LIGHT & USES: Lenses

Concave Lenses Vision Eye is a convex lens. Nearsightedness Concave lenses expand focal lengths Farsightedness Convex lenses shortens the focal length. LIGHT & USES: Optical Instruments Cameras

Telescopes Microscopes 2000 Microsoft Clip Gallery 2000 Microsoft Clip Gallery 2000 Microsoft Clip Gallery LIGHT & USES: Optical

Instruments LASERS Acronym: Light Amplification by Stimulated Emission of Radiation Coherent Light Waves are in phase so it is VERY powerful & VERY intense. LIGHT & USES: Optical Instruments

LASERS Holography Use of Lasers to create 3-D images Fiber Optics Light energy transferred through long, flexible fibers of glass/plastic Uses Communications, medicine, t.v. transmission, data processing. B. Refraction Refraction

bending of waves when passing from one medium to another caused by a change in speed slower (more dense) light bends toward the normal faster (less dense) light bends away from the normal SLOWER

FASTER B. Refraction Refraction depends on speed of light in the medium wavelength of the light - shorter wavelengths (blue) bend more

B. Refraction Example: View explanation. C. Diffraction Diffraction bending of waves around a barrier

longer wavelengths (red) bend more opposite of refraction D. Interference Interference constructive brighter light destructive dimmer light Ch. 15 Sound & Light II. Light and Color

Light and Matter Seeing Colors Mixing Colors A. Light and Matter Opaque absorbs or reflects all light Color you see is the color it reflects Transparent allows light to pass through completely

Color you see is color that is transmitted, all others are absorbed Translucent allows some light to pass through B. Seeing Colors White light contains all visible colors - ROY G. BIV In white light, an object reflects the color you see

absorbs all other colors REFLECTS ALL COLORS ABSORBS ALL COLORS B. Seeing Colors The Retina: Stimulates red & green cones

Lens refracts light to converge on the retina. Nerves transmit the image The retina contains Rods - dim light, black & white Cones - color red - absorb red & yellow green - absorb yellow & green blue - absorb blue & violet Stimulates all cones

B. Seeing Colors Color Blindness one or more sets of cones does not function properly Test for red-green color blindness. C. Mixing Colors Primary

light colors red, green, blue additive colors combine to form white light EX: computer RGBs View Java Applet on primary light colors. Seeing colour The colour an object appears depends on the colours of light it reflects.

For example, a red book only reflects red light: White light Only red light is reflected A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):

Purple light A white hat would reflect all seven colours: White light C. Mixing Colors Filter

transparent material that absorbs all light colors except the filter color View Java Applet on filters. Using filters Filters can be used to block out different colours of light: Red

Filter Magenta Filter C. Mixing Colors Pigment colored material that absorbs and reflects different colors Primary pigment colors

cyan, magenta, yellow subtractive colors combine to form black EX: color ink cartridges C. Mixing Colors Light: RGB Pigment: CMYK

When mixing pigments, the color of the mixture is the color of light that both pigments reflect. C. Mixing Colors RGB (light colors) Red + Green= Yellow Red + Blue = Magenta Green + Blue = Cyan

R+G+ B = White No light = Black What ever you need to mix gets reflected, whatever you dont need gets absorbed Example: Cyan Reflects blue and green, Absorbs Red C. Mixing Colors CMYK (pigment colors) C+M=blue

C+Y=green M+Y=red C+M+Y= Black (K) No Pigment= white What ever you need to mix gets reflected, whatever you dont need gets absorbed Example: Green reflects cyan and yellow; absorbs magenta

Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color. LIGHT & ITS USES 2000 Microsoft Clip Gallery Sources of Light Incandescent light light produced by

heating an object until it glows. 2000 Microsoft Clip Gallery LIGHT & ITS USES 2000 Microsoft Clip Gallery Fluorescent Light Light produced by electron

bombardment of gas molecules Phosphors absorb photons that are created when mercury gas gets zapped with electrons. The phosphors glow & produce light. LIGHT & ITS USES - Neon Neon light neon inside glass tubes makes red light.

Other gases make other colors. 2000 Microsoft Clip Gallery E. Cool Applications! Fiber Optics Total Internal Reflection when all light is reflected back into the denser medium

E. Cool Applications! The Broken Pencil refraction View animation and explanation of the Broken Pencil. E. Cool Applications! Rainbows refraction-reflection-refraction

E. Cool Applications! Diffraction Gratings glass or plastic made up of many tiny parallel slits may also be reflective spectroscopes, reflective rainbow stickers, CD surfaces E. Cool Applications!

Thin Films - Bubbles & Oil Slicks interference results from double reflection E. Cool Applications! Blue Sky & Red Sunsets Molecules in atmosphere scatter light rays. Shorter wavelengths (blue, violet) are scattered more easily.

SUNSET more atmosphere more scattering orange-red sky & sun NOON less atmosphere less scattering blue sky, yellow sun

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