Chapter 25

1. Chapter 25 0 Electromagnetic Induction and Electromagnetic Waves

2. 25 Electromagnetic Induction and Electromagnetic Waves Slide 25-2

3. Slide 25-3

4. Slide 25-4

5. Electromagnetic Induction Slide 25-11

6. Motional emf Slide 25-12

7. Induced Current in a Circuit Slide 25-13

8. Magnetic Flux Slide 25-14

9. Magnetic Flux video that helped Steve R. of PH204 summer session II 2012 • Ok wow, I'm super special and I completly forgot to add the link for the video lol.  Here it is: http://www.youtube.com/watch?v=pB7oZNBIqqc

10. Checking Understanding • A loop of wire of area A is tipped at an angle to a uniform magnetic field B. The maximum flux occurs for an angle . What angle will give a flux that is ½ of this maximum value? •  30 •  45 •  60 •  90 Slide 25-15

11. Answer • A loop of wire of area A is tipped at an angle to a uniform magnetic field B. The maximum flux occurs for an angle . What angle will give a flux that is ½ of this maximum value? •  30 •  45 •  60 •  90 Slide 25-16

12. Lenz’s Law Slide 25-17

13. Slide 25-18

14. Checking Understanding A long conductor carrying a current runs next to a loop of wire. The current in the wire varies as in the graph. Which segment of the graph corresponds to the largest induced current in the loop? Slide 25-19

15. Answer A long conductor carrying a current runs next to a loop of wire. The current in the wire varies as in the graph. Which segment of the graph corresponds to the largest induced current in the loop? E Slide 25-20

16. Checking Understanding • A magnetic field goes through a loop of wire, as below. If the magnitude of the magnetic field is increasing, what can we say about the current in the loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-21

17. Answer • A magnetic field goes through a loop of wire, as below. If the magnitude of the magnetic field is increasing, what can we say about the current in the loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-22

18. Checking Understanding • A magnetic field goes through a loop of wire, as below. If the magnitude of the magnetic field is decreasing, what can we say about the current in the loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-23

19. Answer • A magnetic field goes through a loop of wire, as below. If the magnitude of the magnetic field is decreasing, what can we say about the current in the loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-24

20. Checking Understanding • A magnetic field goes through a loop of wire, as below. If the magnitude of the magnetic field is constant, what can we say about the current in the loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-25

21. Answer • A magnetic field goes through a loop of wire, as below. If the magnitude of the magnetic field is constant, what can we say about the current in the loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-26

22. Checking Understanding • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Just before the switch is closed, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-27

23. Answer • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Just before the switch is closed, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-28

24. Checking Understanding • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Immediately after the switch is closed, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-29

25. Answer • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Immediately after the switch is closed, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-30

26. Checking Understanding • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Long after the switch is closed, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-31

27. Answer • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Immediately after the switch is closed, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-32

28. Checking Understanding • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Immediately after the switch is reopened, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-33

29. Answer • A battery, a loop of wire, and a switch make a circuit below. A second loop of wire sits directly below the first. Immediately after the switch is reopened, what can we say about the current in the lower loop? • The loop has a clockwise current. • The loop has a counterclockwise current. • The loop has no current. Slide 25-34

30. Eddy Currents Slide 25-35

31. Faraday’s Law Slide 25-36

32. Faraday’s Law of Induction • Wikipedia Farady’s Law of Induction

33. Example Problems The figure shows a 10-cm-diameter loop in three different magnetic fields. Theloop’s resistance is 0.1 Ω. For each situation, determine the magnitude and direction of the induced current. A coil used to produce changing magnetic fields in a TMS (transcranial magnetic field stimulation) device produces a magnetic field that increases from 0 T to 2.5 T in a time of 200 s. Suppose this field extends throughout the entire head. Estimate the size of the brain and calculate the induced emf in a loop around the outside of the brain. Slide 25-37

34. Induced Fields A changing magnetic field induces an electric field. A changing electric field induces a magnetic field too. Slide 25-38

35. Electromagnetic Waves Slide 25-39

36. Checking Understanding • A plane electromagnetic wave has electric and magnetic fields at all points in the plane as noted below. With the fields oriented as shown, the wave is moving A. into the plane of the paper. B. out of the plane of the paper. C. to the left. D. to the right. E. toward the top of the paper. Slide 25-40

37. Answer • A plane electromagnetic wave has electric and magnetic fields at all points in the plane as noted below. With the fields oriented as shown, the wave is moving A. into the plane of the paper. B. out of the plane of the paper. C. to the left. D. to the right. E. toward the top of the paper. Slide 25-41

38. Intensity of an Electromagnetic Wave Slide 25-42

39. Example Problems: Electromagnetic Waves Carry Energy Inside the cavity of a microwave oven, the 2.4 GHz electromagnetic waves have an intensity of 5.0 kW/m2. What is the strength of the electric field? The magnetic field? 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? Slide 25-43

40. Polarization Slide 25-44

41. Example Problem Light passed through a polarizing filter has an intensity of 2.0 W/m2. How should a second polarizing filter be arranged to decrease the intensity to 1.0 W/m2? Slide 25-45

42. The Electromagnetic Spectrum Slide 25-46

43. The Photon Model of Electromagnetic Waves Slide 25-47

44. Example Problems A gamma ray has a frequency of 2.4  1020 Hz. What is the energy of an individual photon? A typical digital cell phone emits radio waves with a frequency of 1.9 GHz. What is the wavelength, and what is the energy of individual photons? If the phone emits 0.60 W, how many photons are emitted each second? Slide 25-48

45. Example Problem: The Microwave Oven • Inside the cavity of a microwave oven, the 2.4 GHz electromagnetic waves have an intensity of 5.0 kW/m2. • What is the strength of the electric field? • The magnetic field? Slide 25-49

46. Thermal Emission Spectrum Slide 25-50

47. Understanding Global Warming with Wien’s Law and the Stephan-Boltzmann Law and spectal absorption in the atmosphere.

48. Understanding Global Warming with Wien’s Law and the Stephan-Boltzmann Law and spectal absorption in the atmosphere.

49. Hunting with Thermal Radiation Slide 25-51

50. Seeing the Universe in a Different Light Slide 25-52