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1. 1. PHY138 – Waves, Lecture 6 Today’s overview <ul><li>Waves in the Electric and Magnetic Fields </li></ul><ul><li>The Electromagnetic Spectrum </li></ul><ul><li>The Special Properties of Laser Light </li></ul>
2. 2. Reading Assignment <ul><li>Please read the following from Serway and Jewett before class on Monday: Chapter 25 , Sections 25.1 through 25.4. </li></ul><ul><li>A www.masteringphysics.com assignment is due this Friday at 5:00 PM. It is based on Chapter 14 material: interference, standing waves and harmonics. </li></ul>
3. 3. Note from last day’s lecture: <ul><li>For a standing wave of sound in an air column, the pressure nodes correspond to displacement antinodes . Conversely, the pressure antinodes correspond to displacement nodes . </li></ul><ul><li>It is the pressure variations which cause a microphone or eardrum to vibrate. Therefore, the standing wave sounds loudest near the pressure antinodes, or displacement nodes. </li></ul><ul><li>(this can be discovered in the “Standing Waves and Acoustic Resonance” Lab) </li></ul>
4. 4. Pair 1 Pair 2 The traces above show beats that occur when two different pairs of waves are added. For which of the two is the difference in frequency of the original waves greater? 1. Pair 1 2. Pair 2 3. The frequency difference is the same for both. 4. Need more information.
5. 5. Pair 1 Pair 2 The traces above show beats that occur when two different pairs of waves are added. For which of the two is the sum in frequency of the original waves greater? 1. Pair 1 2. Pair 2 3. The frequency sum is the same for both. 4. Need more information.
6. 6. Which of these thingies are not the same? Heat Microwaves Sound Light Radio Infrared Ultraviolet X-rays Electromagnetic Waves
7. 7. Everything you need to know about Electricity and Magnetism (for now…) = Electric Field, which produces a force on charged objects. Units are Newtons/Coulomb, where “Coulomb” is a measure of electric charge. = Magnetic Field, which causes compasses to point, and produces a force on moving charged objects. Units are called “Tesla”.
8. 8. Results of Maxwell’s Equations: The Wave Equation for Electric Field. The Wave Equation for Magnetic Field. c is a new constant of the universe: c = 2.998 ×10 8 metres/second.
9. 9. Results of Maxwell’s Equations: The relating equations between Electric and Magnetic fields in an electromagnetic wave. c is a constant of the universe: c = 2.998 ×10 8 metres/second.
10. 10. The Electromagnetic Spectrum <ul><li>Radio </li></ul><ul><li>Microwaves </li></ul><ul><li>Infrared Waves </li></ul><ul><li>Visible Light </li></ul><ul><li>Ultraviolet Light </li></ul><ul><li>X-rays </li></ul><ul><li>Gamma Rays </li></ul>higher frequency longer wavelength act more like waves act more like particles
11. 11. “Lasers” <ul><li>L ight A mplified by S timulated E mission R adiation </li></ul><ul><li>Eye surgery: corneal transplants, vision correction </li></ul><ul><li>Heart surgery </li></ul><ul><li>Laser imaging for diagnosis </li></ul><ul><li>Laser dentistry </li></ul>