1. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electromagnetic induction Lenz’s law Faraday’s law The nature of electromagnetic waves The spectrum of electromagnetic waves Electromagnetic Induction and Electromagnetic Waves Topics: Sample question: The ultraviolet view of the flowers on the right shows markings that cannot be seen in the visible region of the spectrum. Whose eyes are these markings intended for? Slide 25-1

2. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Faraday’s Law Slide 25-15

3. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Using Lenz’s Law Slide 25-14

4. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 2.The outer coil of wire is 10 cm long, 2 cm in diameter, wrapped tightly with one layer of 0.5-mm-diameter wire, and has a total resistance of 1.0 Ω. It is attached to a battery, as shown, that steadily decreases in voltage from 12 V to 0 V in 0.5 s, then remains at 0 V for t > 0.5 s. The inner coil of wire is 1 cm long, 1 cm in diameter, has 10 turns of wire, and has a total resistance of 0.01 Ω. It is connected, as shown, to a current meter. a.As the voltage to the outer coil begins to decrease, in which direction (left-to-right or right-to-left) does current flow through the meter? Explain. b.Draw a graph showing the current in the inner coil as a function of time for 0 ≤ t ≤ 1 s. Include a numerical scale on the vertical axis. Slide 25-55 Additional Examples

5. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 21.6 Back EMF and Counter Torque; Eddy Currents Induced currents can flow in bulk material as well as through wires. These are called eddy currents, and can dramatically slow a conductor moving into or out of a magnetic field.

6. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electromagnetic Waves Slide 25-33

7. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Maxwell established the following properties of electromagnetic waves 1)Electromagnetic waves are transverse waves 2)Electromagnetic waves can exist at any frequency, not just the frequencies of visible light. 3)Electromagnetic waves travel in a vacuum with the 4)At any point on the wave, the electric and magnetic fields are related by E = cB Electromagnetic Waves Slide 25-36

8. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 1)Inside the cavity of a microwave oven, the 2.4 GHz electromagnetic waves have an intensity of 5.0 kW/m 2. What is the strength of the electric field? The magnetic field? 2)A digital cell phone emits a 1.9 GHz electromagnetic wave with total power 0.60 W. At a cell phone tower 2.0 km away, what is the intensity of the wave? (Assume that the wave spreads out uniformly in all directions.) What are the electric and magnetic field strengths at this distance? Electromagnetic Waves Carry Energy Slide 25-36

9. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Polarization Slide 25-37

10. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Light passed through a polarizing filter has an intensity of 2.0 W/m 2. How should a second polarizing filter be arranged to decrease the intensity to 1.0 W/m 2 ? Slide 25-38

11. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Electromagnetic Spectrum Slide 25-39

12. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 1.When an object like a tree is illuminated by the sun, and you are looking toward the tree, light rays leave the object A.only from points at the top and base of the tree, but in every direction. B.from every point on the surface of the tree, but only toward your eyes. C.only from points at the top and base of the tree, but only toward your eyes D.from every point on the surface of the tree and in every direction. Slide 18-2

13. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 1.When an object like a tree is illuminated by the sun, and you are looking toward the tree, light rays leave the object D.from every point on the surface of the tree and in every direction. Slide 18-3 Answer

14. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 2. A light ray can change direction when going from one material into another. This phenomenon is known as A.reflection. B.absorption. C.refraction. D.scattering. Slide 18-4

15. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 2. A light ray can change direction when going from one material into another. This phenomenon is known as C.refraction. Slide 18-5 Answer

16. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Ray Model of Light Light rays travel in straight lines. Light rays can cross. A light ray travels forever unless it interacts with matter. An object is a source of light rays.The eye sees by focusing a bundle of rays. Slide 18-6

17. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Sources of Light Rays: Self-Luminous Objects A ray sourceA point source An extended source A parallel-ray source Slide 18-7

18. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Seeing Objects Seeing a ray source Seeing an object by scattered light Seeing a point or extended source Slide 18-8

19. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Shadows Slide 18-9

20. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Law of Reflection Slide 18-12 1.The incident ray and the reflected ray are in the same plane normal to the surface, and 2.The angle of reflection equals the angle of incidence: θ r = θ i.

21. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Plane Mirror Slide 18-13

22. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Refraction Slide 18-14

23. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Snell’s Law of Refraction Slide 18-15

24. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 18-16

25. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. What is the index of refraction of the plastic if a ray is refracted as in the figure? Example Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 18-17

26. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Total Internal Reflection Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 18-18