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Table of Contents

Chapter 20. Electromagnetic Induction. Table of Contents. Section 1 Electricity from Magnetism Section 2 Generators, Motors, and Mutual Inductance Section 3 AC Circuits and Transformers Section 4 Electromagnetic Waves. Section 1 Electricity from Magnetism. Chapter 20.

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  1. Chapter 20 Electromagnetic Induction Table of Contents Section 1 Electricity from Magnetism Section 2 Generators, Motors, and Mutual Inductance Section 3 AC Circuits and Transformers Section 4 Electromagnetic Waves

  2. Section 1 Electricity from Magnetism Chapter 20 Objectives • Recognizethat 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. • ApplyLenz’s law and Faraday’s law of induction to solve problems involving induced emf and current.

  3. Section 1 Electricity from Magnetism Chapter 20 Electromagnetic Induction • Electromagnetic inductionis 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. Section 1 Electricity from Magnetism Chapter 20 Electromagnetic Induction in a Circuit Loop

  5. 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.

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

  7. Section 1 Electricity from Magnetism Chapter 20 Characteristics of Induced Current • Lenz’s Law 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. Section 1 Electricity from Magnetism Chapter 20 Lenz's Law for Determining the Direction of the Induced Current

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

  10. 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. 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 q = 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. 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. 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. 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. 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. 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. Section 2 Generators, Motors, and Mutual Inductance Chapter 20 Objectives • Describehow generators and motors operate. • Explainthe energy conversions that take place in generators and motors. • Describehow mutual induction occurs in circuits.

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

  19. Section 2 Generators, Motors, and Mutual Inductance Chapter 20 Induction of an emf in an AC Generator

  20. Section 2 Generators, Motors, and Mutual Inductance Chapter 20 Function of a Generator

  21. 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.

  22. Section 2 Generators, Motors, and Mutual Inductance Chapter 20 Comparing AC and DC Generators

  23. 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.

  24. Section 2 Generators, Motors, and Mutual Inductance Chapter 20 DC Motors

  25. 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:

  26. Section 2 Generators, Motors, and Mutual Inductance Chapter 20 Mutual Inductance

  27. Section 3 AC Circuits and Transformers Chapter 20 Objectives • Distinguishbetween rms values and maximum values of current and potential difference. • Solveproblems involving rms and maximum values of current and emf for ac circuits. • Applythe transformer equation to solve problems involving step-up and step-down transformers.

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

  29. 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.

  30. Section 3 AC Circuits and Transformers Chapter 20 rms Current

  31. 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= ?

  32. 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 = 0.707 ∆Vmax Rearrange the definition for resistance to calculate Irms. • Use the equation for rms current to find Irms. • Irms = 0.707 Imax

  33. 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.

  34. 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. 4. Evaluate The rms values for emf and current are a little more than two-thirds the maximum values, as expected.

  35. Section 3 AC Circuits and Transformers Chapter 20 Transformers • Atransformeris 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.

  36. Section 3 AC Circuits and Transformers Chapter 20 Transformers

  37. 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.

  38. Section 3 AC Circuits and Transformers Chapter 20 A Step-Up Transformer in an Auto Ignition System

  39. Section 4 Electromagnetic Waves Chapter 20 Objectives • Describewhat electromagnetic waves are and how they are produced. • Recognizethat electricity and magnetism are two aspects of a single electromagnetic force. • Explainhow electromagnetic waves transfer energy. • Describevarious applications of electromagnetic waves.

  40. 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 aretransverse 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 theelectromagnetic force.

  41. Section 4 Electromagnetic Waves Chapter 20 Electromagnetic Waves

  42. 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. Electromagneticradiation varies periodically and travels at the speed of light.

  43. Section 4 Electromagnetic Waves Chapter 20 The Sun at Different Wavelengths of Radiation

  44. 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 thewave-particle duality. • Aphotonis 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.

  45. 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.

  46. 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 Section 4 Electromagnetic Waves Chapter 20 The Electromagnetic Spectrum, continued

  47. Section 4 Electromagnetic Waves Chapter 20 The Electromagnetic Spectrum

  48. Section 1 Electricity from Magnetism Chapter 20 Ways of Inducing a Current in a Circuit

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