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Light and the Electromagnetic Spectrum Chapters 22 & 23 MAP TAP 2003-2004 The Electromagnetic Spectrum 1 LIGHT: What Is It? © 2000 Microsoft Clip Gallery • Light Energy – Atoms • As atoms absorb energy, electrons jump up 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 MAP TAP 2003-2004 The Electromagnetic Spectrum 2 © 2000 Microsoft Clip Gallery © 2000 Microsoft Clip Gallery • An electromagnetic wave consists of electric and magnetic fields which vibrate thus making waves. • Energy is perpendicular to direction of motion • Moving photon creates electric & magnetic field which are at right angles to each other. MAP TAP 2003-2004 The Electromagnetic Spectrum 3 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 MAP TAP 2003-2004 The Electromagnetic Spectrum 4 © 2000 Microsoft Clip Gallery Light Waves • Properties of light waves include speed, frequency and wavelength • Speed (s), frequency (f) and wavelength (l) are related in the formula l x f = s • All EM waves travel at a speed of 300,000 km/s in a vacuum • EM waves will travel at slower speeds through medium such as air, water and glass MAP TAP 2003-2004 The Electromagnetic Spectrum 5 Wavelength, Frequency and Energy • Light with a short wavelength will have a high frequency and high energy. • Light with long wavelengths have low frequencies and low energy MAP TAP 2003-2004 The Electromagnetic Spectrum 6 Chapter 22 Section 2 The Electromagnetic Spectrum MAP TAP 2003-2004 The Electromagnetic Spectrum 7 MAP TAP 2003-2004 The Electromagnetic Spectrum 8 Electromagnetic Spectrum • The electromagnetic spectrum is the complete spectrum or continuum of light including radio waves, infrared, visible light, ultraviolet light, Xrays and gamma rays MAP TAP 2003-2004 The Electromagnetic Spectrum 9 MAP TAP 2003-2004 The Electromagnetic Spectrum 10 Radio waves • Low energy waves with long wavelengths and low frequencies • Includes FM, AM, radar and TV waves • Used in many devices such as remote control items, cell phones, wireless devices, etc. • AM has longer wavelength, is used for audio portion of TV broadcasts and its long wavelength can bend around hills. MAP TAP 2003-2004 The Electromagnetic Spectrum 11 Modulating Radio Waves • Modulation – variation of amplitude or frequency when waves are broadcast • AM – amplitude modulation • FM - frequency modulation MAP TAP 2003-2004 The Electromagnetic Spectrum 12 AM and FM • AM – carries audio for TV broadcasts and its longer wavelengths bend around hills and tall buildings • FM – carries video for TV broadcasts MAP TAP 2003-2004 The Electromagnetic Spectrum 13 MAP TAP 2003-2004 The Electromagnetic Spectrum 14 Microwaves • First used in radar, now used in communication, medicine and consumer use (microwave ovens) MAP TAP 2003-2004 The Electromagnetic Spectrum 15 Infrared waves • Invisible electromagnetic waves that are detected as heat • Can be detected with special devices such as night goggles • Used in heat lamps MAP TAP 2003-2004 The Electromagnetic Spectrum 16 MAP TAP 2003-2004 The Electromagnetic Spectrum 17 Visible Light • The portion of the electromagnetic spectrum that human eyes can detect • ROY G BIV (red, orange, yellow, green, blue, indigo, violet) • Red is the lowest frequency and violet is the highest frequency MAP TAP 2003-2004 The Electromagnetic Spectrum 18 MAP TAP 2003-2004 The Electromagnetic Spectrum 19 Ultraviolet waves • Higher energy than light waves • Can cause skin cancer and blindness in humans • Used in tanning beds, food processing and sterilizing equipment in hospitals, food processing • Helps your body absorb Vitamin D MAP TAP 2003-2004 The Electromagnetic Spectrum 20 X-Rays • High energy waves • First discovered by Roentgen • Used in medicine, industry and astronomy • Can cause cancer • Bones absorb x-rays but soft tissue does not • Lead absorbs X-rays MAP TAP 2003-2004 The Electromagnetic Spectrum 21 Gamma rays • • • • Highest energy Shortest wavelength Come from outer space Blocked from Earth’s surface by atmosphere • Can be used in cancer treatments MAP TAP 2003-2004 The Electromagnetic Spectrum 22 MAP TAP 2003-2004 The Electromagnetic Spectrum 23 Time to think….. • 1. What is the relationship between frequency and wavelength? • 2. What is meant by ‘spectrum’? • 3. What does ROY G BIV mean? MAP TAP 2003-2004 The Electromagnetic Spectrum 24 Now, let’s really think • 4. Can you actually see x-rays? – Support your answer. • 5. Which color is more energetic, red or yellow? • 6. Which type of wave travels faster, gamma or radio? • 7. Why are microwaves more dangerous than radio waves? MAP TAP 2003-2004 The Electromagnetic Spectrum 25 Think about it…. • You have just been involved in a traffic incident that leaves you stranded on the side of the road. Which part of the electromagnetic spectrum would be of the most use to you and why? MAP TAP 2003-2004 The Electromagnetic Spectrum 26 Answers • 1. Frequency and wavelength are properties of waves and since speed is constant for EM waves, as frequency increases, wavelength decreases. • 2. Spectrum is a continuum of all electromagnetic waves • 3, ROY G BIV is the difference colors of the visible light in order of longest wavelength to shortest wavelength. • 4. X-rays can not be seen, only the waves in the visible light portion are visible. • 5. Yellow is higher energy than red because it has a shorter wavelength and higher frequency. • 6. Both travel at the same speed, 300,000 km/s (all em waves travel at the same speed) • 7. Microwaves have a higher frequency than radio and carry more energy. MAP TAP 2003-2004 The Electromagnetic Spectrum 27 Chapter 22 Section 3 Interactions of Light MAP TAP 2003-2004 The Electromagnetic Spectrum 28 Refraction of Light • Refraction – Bending of light due to a change in speed. – Index of Refraction – Amount by which a material refracts light. – Prisms – Glass that bends light. Different frequencies are bent different amounts & light is broken out into different colors. MAP TAP 2003-2004 The Electromagnetic Spectrum 29 Refraction – bending of light MAP TAP 2003-2004 The Electromagnetic Spectrum 30 Diffraction & Refraction • Diffraction – Bending of waves around the edge of a barrier. New waves are formed from the original. breaks images into bands of light & dark and colors. • Refraction – Bending of waves due to a change in speed through an object. MAP TAP 2003-2004 The Electromagnetic Spectrum 31 LIGHT & USES: Diffraction © 2000 Microsoft Encarta • A diffraction grating. Each space between the ruled grooves acts as a MAP TAPThe 2003-2004 The Electromagnetic 32 slit. light bends around the edgesSpectrum and gets refracted. Reflection • Reflection – Bouncing back of light waves – Regular reflection – mirrors smooth surfaces scatter light very little. Images are clear & exact. – Diffuse reflection – reflected light is scattered due to an irregular surface. MAP TAP 2003-2004 The Electromagnetic Spectrum 33 Chapter 22 Section 4 Light and Color MAP TAP 2003-2004 The Electromagnetic Spectrum 34 Color of Light • Transparent Objects: © 2000 Microsoft Clip Gallery – Light transmitted because of no scattering – Color transmitted is color you see. All other colors are absorbed. • Translucent: – Light is scattered and transmitted some. • Opaque: – Light is either reflected or absorbed. – Color of opaque objects is color it reflects. MAP TAP 2003-2004 The Electromagnetic Spectrum 35 Color of Light (Cont.) • Color of Objects – White light is the presence of ALL the colors of the visible spectrum. – Black objects absorb ALL the colors and no light is reflected back. MAP TAP 2003-2004 The Electromagnetic Spectrum 36 © 2000 Microsoft Clip Gallery Color of Light (Cont.) © 2000 Microsoft Clip Gallery • Primary Colors of Light – Three colors that can be mixed to produce any other colored light – Red + blue + green = white light • Complimentary Colors of Light – Two complimentary colors combine to make white light-Magenta,Cyan,Yellow MAP TAP 2003-2004 The Electromagnetic Spectrum 37 Paint Pigments © 2000 Microsoft Clip Gallery – Pigments absorb the frequency of light that you see – Primary pigments • Yellow + cyan + magenta = black • Primary pigments are compliments of the primary colors of light. MAP TAP 2003-2004 The Electromagnetic Spectrum 38 Complementary Pigments © 2000 Microsoft Clip Gallery • Green, blue, red • Complimentary pigments are primary colors for light! MAP TAP 2003-2004 The Electromagnetic Spectrum © 2000 Microsoft Clip Gallery 39 Chapter 23 Section 1 Mirrors and Lenses MAP TAP 2003-2004 The Electromagnetic Spectrum 40 • Enlarged – © 2000 Microsoft Clip Gallery – Image is larger than actual object. • Reduced – – Image is smaller than object. MAP TAP 2003-2004 The Electromagnetic Spectrum © 2000 Microsoft Clip Gallery 41 © 2000 Microsoft Clip Gallery • Erect – – Image is right side up. • Inverted – – Image is upside down. MAP TAP 2003-2004 The Electromagnetic Spectrum 42 © 2000 Microsoft Clip Gallery L • Real Image – – Image is made from “real” light rays that converge at a real focal point so the image is REAL – Can be projected onto a screen because light actually passes through the point where the image appears – Always inverted MAP TAP 2003-2004 The Electromagnetic Spectrum 43 • Virtual Image– – “Not Real” because it cannot be projected – Image only seems to be there! MAP TAP 2003-2004 The Electromagnetic Spectrum 44 Mirrors © 2000 Microsoft Clip Gallery – 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 MAP TAP 2003-2004 The Electromagnetic Spectrum 45 Mirrors • Plane Mirrors – Perfectly flat – Virtual – Image is “Not Real” because it cannot be projected – Erect – Image is right side up MAP TAP 2003-2004 The Electromagnetic Spectrum 46 © 2000 Microsoft Clip Gallery – Convex Mirror • Curves outward • Enlarges images. – Use: Rear view mirrors, store security… CAUTION! Objects are closer than theySpectrum appear! MAP TAP 2003-2004 The Electromagnetic 47 © 2000 Microsoft Clip Gallery 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 MAP TAP 2003-2004 The Electromagnetic Spectrum 48 LIGHT & ITS USES: Lenses • Convex Lenses • Ray Tracing Focal Point Object © 2000 D. L. Power Lens – Two rays usually define an image • Ray #1: Light ray comes from top of object; travels parallel to optic axis; bends thru focal point. MAP TAP 2003-2004 The Electromagnetic Spectrum 49 LIGHT & ITS USES: Lenses • Convex Lenses • Ray Tracing Ray #1 © 2000 D. L. Power – Two rays define an image Ray #2 • Ray 2: Light ray comes from top of object & travels through center of lens. MAP TAP 2003-2004 The Electromagnetic Spectrum 50 Concave Lenses © 2000 D. L. Power Lens that is thicker at the edges and thinner in the center. – Diverges light rays – All images are erect and reduced. MAP TAP 2003-2004 The Electromagnetic Spectrum 51 Chapter 23 Section 2 Light and Sight MAP TAP 2003-2004 The Electromagnetic Spectrum 52 MAP TAP 2003-2004 The Electromagnetic Spectrum 53 How You See © 2000 Microsoft Clip Gallery • Retina – – Lens refracts light to converge on the retina. Nerves transmit the image • Rods – – Nerve cells in the retina. Very sensitive to light & dark • Cones – – Nerve cells help to see light/color MAP TAP 2003-2004 The Electromagnetic Spectrum 54 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. MAP TAP 2003-2004 The Electromagnetic Spectrum © 2000 Microsoft Clip Gallery © 2000 Microsoft Clip Gallery 55 Eye is a convex lens • Nearsightedness – Concave lenses expand focal lengths • Farsightedness – Convex lenses shortens the focal length. MAP TAP 2003-2004 The Electromagnetic Spectrum 56 Chapter 23 Section 3 Light and Technology MAP TAP 2003-2004 The Electromagnetic Spectrum 57 LIGHT & ITS USES © 2000 Microsoft Clip Gallery • Sources of Light – Incandescent light – light produced by heating an object until it glows. MAP TAP 2003-2004 The Electromagnetic Spectrum 58 © 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. MAP TAP 2003-2004 The Electromagnetic Spectrum 59 LIGHT & ITS USES - Neon • Neon light – neon inside glass tubes makes red light. Other gases make other colors. MAP TAP 2003-2004 The Electromagnetic Spectrum © 2000 Microsoft Clip Gallery 60 LIGHT & USES: Optical Instrument • Cameras • Telescopes • Microscopes © 2000 Microsoft Clip Gallery MAP TAP 2003-2004 The Electromagnetic Spectrum © 2000 Microsoft Clip Gallery 61 © 2000 Microsoft Clip Gallery Telescopes • Refracting telescopes – use two convex lenses • Reflecting telescopes use a concave mirror to bounce the light to a plane mirror which reflects the light to a convex lenses MAP TAP 2003-2004 The Electromagnetic Spectrum 62 LIGHT & USES: Optical Instrument • LASERS – Acronym: Light Amplification by Stimulated Emission of Radiation – Coherent Light – Waves are in phase so it is VERY powerful & VERY intense. MAP TAP 2003-2004 The Electromagnetic Spectrum 63 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. MAP TAP 2003-2004 The Electromagnetic Spectrum 64 Polarized Light • Light waves vibrate in only one plane or direction. Can cause glare. Be sure your sunglasses are polarized to reduce the glare. MAP TAP 2003-2004 The Electromagnetic Spectrum 65 Communication Technology • Cordless phone – phone & radio signals • Cellular phone – mainly uses microwaves to send signals • Satellite TV – uses microwaves • Global Positioning System (GPS) – uses microwaves and satellite system (24) – need a signal from at least 4 satellites to find a location. MAP TAP 2003-2004 The Electromagnetic Spectrum 66