1. Chapter 20 Preview Objectives Electromagnetic Induction
Section 1 Electricity from Magnetism
Chapter 20
Preview
Objectives
Electromagnetic Induction
Characteristics of Induced Current
Sample Problem
Link each section title to the first page of that section (“Objectives”)

2. Section 1 Electricity from Magnetism
Chapter 20
Objectives
Recognize that relative motion between a conductor and a magnetic field induces an emf in the conductor.
Describe how the change in the number of magnetic field lines through a circuit loop affects the magnitude and direction of the induced electric current.
Apply Lenz’s law and Faraday’s law of induction to solve problems involving induced emf and current.

3. Electromagnetic Induction
Section 1 Electricity from Magnetism
Chapter 20
Electromagnetic Induction
Electromagnetic induction is the process of creating a current in a circuit by a changing magnetic field.
A change in the magnetic flux through a conductor induces an electric current in the conductor.
The separation of charges by the magnetic force induces an emf.

4. Electromagnetic Induction in a Circuit Loop
Section 1 Electricity from Magnetism
Chapter 20
Electromagnetic Induction in a Circuit Loop
Insert High-Res image from Figure 1, page 708

5. Electromagnetic Induction, continued
Section 1 Electricity from Magnetism
Chapter 20
Electromagnetic Induction, continued
The angle between a magnetic field and a circuit affects induction.
A change in the number of magnetic field lines induces a current.
Insert High-Res art from Figure 3 page 709

6. Ways of Inducing a Current in a Circuit
Section 1 Electricity from Magnetism
Chapter 20
Ways of Inducing a Current in a Circuit
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Visual Concept

7. Characteristics of Induced Current
Section 1 Electricity from Magnetism
Chapter 20
Characteristics of Induced Current
Lenz’s Law
states that the magnetic field of an induced current opposes a change in the applied magnetic field. 
The magnetic field of the induced current is in a direction to produce a field that opposes the change causing it.
Note: the induced current does not oppose the applied field, but rather the change in the applied field.

8. Lenz's Law for Determining the Direction of the Induced Current
Section 1 Electricity from Magnetism
Chapter 20
Lenz's Law for Determining the Direction of the Induced Current
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Visual Concept

9. Characteristics of Induced Current, continued
Section 1 Electricity from Magnetism
Chapter 20
Characteristics of Induced Current, continued
The magnitude of the induced emf can be predicted by Faraday’s law of magnetic induction.
Faraday’s Law of Magnetic Induction
The magnetic flux is given by M = Abcos.

10. Chapter 20 Sample Problem Induced emf and Current
Section 1 Electricity from Magnetism
Chapter 20
Sample Problem
Induced emf and Current
A coil with 25 turns of wire is wrapped around a hollow tube with an area of 1.8 m2. Each turn has the same area as the tube. A uniform magnetic field is applied at a right angle to the plane of the coil. If the field increases uniformly from 0.00 T to 0.55 T in 0.85 s, find the magnitude of the induced emf in the coil. If the resistance in the coil is 2.5 Ω, find the magnitude of the induced current in the coil.

11. Sample Problem, continued
Section 1 Electricity from Magnetism
Chapter 20
Sample Problem, continued
Induced emf and Current
1. Define
Given:
∆t = 0.85 s A = 1.8 m2  = 0.0º
N = 25 turns R = 2.5 Ω
Bi = 0.00 T = 0.00 V•s/m2
Bf = 0.55 T = 0.55 V•s/m2
Unknown:
emf = ?
I = ?

12. Sample Problem, continued
Section 1 Electricity from Magnetism
Chapter 20
Sample Problem, continued
Induced emf and Current
1. Define, continued
Diagram: Show the coil before and after the change in the magnetic field.

13. Sample Problem, continued
Section 1 Electricity from Magnetism
Chapter 20
Sample Problem, continued
Induced emf and Current
2. Plan
Choose an equation or situation. Use Faraday’s law of magnetic induction to find the induced emf in the coil.
Substitute the induced emf into the definition of resistance to determine the induced current in the coil.

14. Sample Problem, continued
Section 1 Electricity from Magnetism
Chapter 20
Sample Problem, continued
Induced emf and Current
2. Plan, continued
Rearrange the equation to isolate the unknown. In this example, only the magnetic field strength changes with time. The other components (the coil area and the angle between the magnetic field and the coil) remain constant.

15. Sample Problem, continued
Section 1 Electricity from Magnetism
Chapter 20
Sample Problem, continued
Induced emf and Current
3. Calculate
Substitute the values into the equation and solve.

16. Sample Problem, continued
Section 1 Electricity from Magnetism
Chapter 20
Sample Problem, continued
Induced emf and Current
4. Evaluate
The induced emf, and therefore the induced current, is directed through the coil so that the magnetic field produced by the induced current opposes the change in the applied magnetic field. For the diagram shown on the previous page, the induced magnetic field is directed to the right and the current that produces it is directed from left to right through the resistor.

17. Chapter 20 Preview Objectives Generators and Alternating Current
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Preview
Objectives
Generators and Alternating Current
Motors
Mutual Inductance

18. Chapter 20 Objectives Describe how generators and motors operate.
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Objectives
Describe how generators and motors operate.
Explain the energy conversions that take place in generators and motors.
Describe how mutual induction occurs in circuits.

19. Generators and Alternating Current
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Generators and Alternating Current
A generator is a machine that converts mechanical energy into electrical energy.
Generators use induction to convert mechanical energy into electrical energy.
A generator produces a continuously changing emf.

20. Induction of an emf in an AC Generator
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Induction of an emf in an AC Generator
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21. Function of a Generator
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Function of a Generator
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Visual Concept

22. Generators and Alternating Current, continued
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Generators and Alternating Current, continued
Alternating current is an electric current that changes direction at regular intervals.
Alternating current can be converted to direct current by using a device called a commutator to change the direction of the current.

23. Comparing AC and DC Generators
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Comparing AC and DC Generators
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Visual Concept

24. Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Motors
Motors are machines that convert electrical energy to mechanical energy.
Motors use an arrangement similar to that of generators.
Back emf is the emf induced in a motor’s coil that tends to reduce the current in the coil of a motor.

25. Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
DC Motors
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Visual Concept

26. Chapter 20 Mutual Inductance
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Mutual Inductance
The ability of one circuit to induce an emf in a nearby circuit in the presence of a changing current is called mutual inductance.
In terms of changing primary current, Faraday’s law is given by the following equation, where M is the mutual inductance:

27. Chapter 20 Mutual Inductance
Section 2 Generators, Motors, and Mutual Inductance
Chapter 20
Mutual Inductance
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Visual Concept

28. Chapter 20 Preview Objectives Effective Current Sample Problem
Section 3 AC Circuits and Transformers
Chapter 20
Preview
Objectives
Effective Current
Sample Problem
Transformers

29. Section 3 AC Circuits and Transformers
Chapter 20
Objectives
Distinguish between rms values and maximum values of current and potential difference.
Solve problems involving rms and maximum values of current and emf for ac circuits.
Apply the transformer equation to solve problems involving step-up and step-down transformers.

30. Chapter 20 Effective Current
Section 3 AC Circuits and Transformers
Chapter 20
Effective Current
The root-mean-square (rms) current of a circuit is the value of alternating current that gives the same heating effect that the corresponding value of direct current does.
rms Current

31. Effective Current, continued
Section 3 AC Circuits and Transformers
Chapter 20
Effective Current, continued
The rms current and rms emf in an ac circuit are important measures of the characteristics of an ac circuit.
Resistance influences current in an ac circuit.

32. Chapter 20 rms Current Section 3 AC Circuits and Transformers
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Visual Concept

33. Chapter 20 Sample Problem rms Current and emf
Section 3 AC Circuits and Transformers
Chapter 20
Sample Problem
rms Current and emf
A generator with a maximum output emf of 205 V is connected to a 115 Ω resistor. Calculate the rms potential difference. Find the rms current through the resistor. Find the maximum ac current in the circuit.
1. Define
Given:
∆Vrms = 205 V R = 115 Ω
Unknown:
∆Vrms = ? Irms = ? Imax = ?

34. Sample Problem, continued
Section 3 AC Circuits and Transformers
Chapter 20
Sample Problem, continued
rms Current and emf
2. Plan
Choose an equation or situation. Use the equation for the rms potential difference to find ∆Vrms.
∆Vrms = ∆Vmax
Rearrange the definition for resistance to calculate Irms.
Use the equation for rms current to find Irms.
Irms = Imax

35. Sample Problem, continued
Section 3 AC Circuits and Transformers
Chapter 20
Sample Problem, continued
rms Current and emf
2. Plan, continued
Rearrange the equation to isolate the unknown. Rearrange the equation relating rms current to maximum current so that maximum current is calculated.

36. Sample Problem, continued
Section 3 AC Circuits and Transformers
Chapter 20
Sample Problem, continued
rms Current and emf
3. Calculate
Substitute the values into the equation and solve. . 7 D = m a x ( ) 2 5 V 1 4 6 A 8 r s I Ω
4. Evaluate The rms values for emf and current are a little more than two-thirds the maximum values, as expected.

37. Section 3 AC Circuits and Transformers
Chapter 20
Transformers
A transformer is a device that increases or decreases the emf of alternating current.
The relationship between the input and output emf is given by the transformer equation.

38. Chapter 20 Transformers Section 3 AC Circuits and Transformers
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Visual Concept

39. Transformers, continued
Section 3 AC Circuits and Transformers
Chapter 20
Transformers, continued
The transformer equation assumes that no power is lost between the primary and secondary coils. However, real transformers are not perfectly efficient.
Real transformers typically have efficiencies ranging from 90% to 99%.
The ignition coil in a gasoline engine is a transformer.

40. A Step-Up Transformer in an Auto Ignition System
Section 3 AC Circuits and Transformers
Chapter 20
A Step-Up Transformer in an Auto Ignition System
Insert High-Res image from TR112

41. Chapter 20 Preview Objectives Propagation of Electromagnetic Waves
Section 4 Electromagnetic Waves
Chapter 20
Preview
Objectives
Propagation of Electromagnetic Waves
The Electromagnetic Spectrum

42. Section 4 Electromagnetic Waves
Chapter 20
Objectives
Describe what electromagnetic waves are and how they are produced.
Recognize that electricity and magnetism are two aspects of a single electromagnetic force.
Explain how electromagnetic waves transfer energy.
Describe various applications of electromagnetic waves.

43. Propagation of Electromagnetic Waves
Section 4 Electromagnetic Waves
Chapter 20
Propagation of Electromagnetic Waves
Electromagnetic waves travel at the speed of light and are associated with oscillating, perpendicular electric and magnetic fields.
Electromagnetic waves are transverse waves; that is, the direction of travel is perpendicular to the the direction of oscillating electric and magnetic fields.
Electric and magnetic forces are aspects of a single force called the electromagnetic force.

44. Electromagnetic Waves
Section 4 Electromagnetic Waves
Chapter 20
Electromagnetic Waves
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Visual Concept

45. Propagation of Electromagnetic Waves, continued
Section 4 Electromagnetic Waves
Chapter 20
Propagation of Electromagnetic Waves, continued
All electromagnetic waves are produced by accelerating charges.
Electromagnetic waves transfer energy. The energy of electromagnetic waves is stored in the waves’ oscillating electric and magnetic fields.
Electromagnetic radiation is the transfer of energy associated with an electric and magnetic field. Electromagnetic radiation varies periodically and travels at the speed of light.

46. The Sun at Different Wavelengths of Radiation
Section 4 Electromagnetic Waves
Chapter 20
The Sun at Different Wavelengths of Radiation
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47. Propagation of Electromagnetic Waves, continued
Section 4 Electromagnetic Waves
Chapter 20
Propagation of Electromagnetic Waves, continued
High-energy electromagnetic waves behave like particles.
An electromagnetic wave’s frequency makes the wave behave more like a particle. This notion is called the wave-particle duality.
A photon is a unit or quantum of light. Photons can be thought of as particles of electromagnetic radiation that have zero mass and carry one quantum of energy.

48. The Electromagnetic Spectrum
Section 4 Electromagnetic Waves
Chapter 20
The Electromagnetic Spectrum
The electromagnetic spectrum ranges from very long radio waves to very short-wavelength gamma waves.
The electromagnetic spectrum has a wide variety of applications and characteristics that cover a broad range of wavelengths and frequencies.

49. The Electromagnetic Spectrum, continued
Section 4 Electromagnetic Waves
Chapter 20
The Electromagnetic Spectrum, continued
Radio Waves
longest wavelengths
communications, tv
Microwaves
30 cm to 1 mm
radar, cell phones
Infrared
1 mm to 700 nm
heat, photography
Visible light
700 nm (red) to 400 nm (violet)
Ultraviolet
400 nm to 60 nm
disinfection, spectroscopy
X rays
60 nm to 10–4 nm
medicine, astronomy, security screening
Gamma Rays
less than 0.1 nm
cancer treatment, astronomy

50. The Electromagnetic Spectrum
Section 4 Electromagnetic Waves
Chapter 20
The Electromagnetic Spectrum
Insert High-Res image from TR114