1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Describe the conditions required for electromagnetic induction. Apply the concept of electromagnetic induction to generators. Explain how transformers increase or decrease voltage across power lines. Section 3 Electric Currents from Magnetism Chapter 17

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Induction and Faraday’s Law Electromagnetic induction is the process of creating a current in a circuit by changing a magnetic field. Faraday’s law states the following: An electric current can be produced in a circuit by a changing magnetic field. As the loop moves in and out of the magnetic field of the magnet, a current is induced in the circuit. Rotating the circuit or changing the strength of the magnetic field will also induce a current in the circuit. Section 3 Electric Currents from Magnetism Chapter 17

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Induction Section 3 Electric Currents from Magnetism Chapter 17

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Induction and Faraday’s Law, continued Electromagnetic induction does not violate the law of conservation of energy. Moving electric charges experience a magnetic force when in a magnetic field. The force is at its maximum value when the charge moves perpendicular to the field. As the angle between the charge’s direction and the direction of the magnetic field decreases, the force on the charge decreases. Section 3 Electric Currents from Magnetism Chapter 17

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Induction When the wire in a circuit moves perpendicular to a magnetic field, the current induced in the wire is at a maximum. When the wire moves parallel to a magnetic field, there is zero current induced in the wire. Section 3 Electric Currents from Magnetism Chapter 17

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Induction and Faraday’s Law, continued A generator is a machine that converts mechanical energy to electrical energy. An alternating current (AC) is an electric current that changes direction at regular intervals. For each half rotation of the loop in an AC generator, the current produced by the generator reverses direction. Generators produce the electrical energy you use in your home. Section 3 Electric Currents from Magnetism Chapter 17

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu AC Generator Section 3 Electric Currents from Magnetism Chapter 17

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Induced Current Section 3 Electric Currents from Magnetism Chapter 17

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Induction and Faraday’s Law, continued Electricity and magnetism are two aspects of a single electromagnetic force. The energy that results from these two forces is called electromagnetic (EM) energy. Light is a form of electromagnetic energy. EM waves are made up of oscillating electric and magnetic fields that are perpendicular to each other. EM waves are also called EMF (electromagnetic frequency) Section 3 Electric Currents from Magnetism Chapter 17

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Wave Section 3 Electric Currents from Magnetism Chapter 17

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 2.What conditions are necessary to induce an electric current? F.A conductor must move past a stationary magnetic field. G.A magnetic field must move past a stationary conductor. H.A conductor and a magnetic field must move relative to one another. I.A magnetic field and a conductor must move together relative to a stationary point. Standardized Test Prep Chapter 17

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 2.What conditions are necessary to induce an electric current? F.A conductor must move past a stationary magnetic field. G.A magnetic field must move past a stationary conductor. H.A conductor and a magnetic field must move relative to one another. I.A magnetic field and a conductor must move together relative to a stationary point. Standardized Test Prep Chapter 17

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 3.What is the result of cutting a bar magnet in half? A.two unmagnetized bars B.two magnets with north poles only C.two smaller magnets with both north and south poles D.one magnet with north poles only and one magnet with south poles only Standardized Test Prep Chapter 17

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 3.What is the result of cutting a bar magnet in half? A.two unmagnetized bars B.two magnets with north poles only C.two smaller magnets with both north and south poles D.one magnet with north poles only and one magnet with south poles only Standardized Test Prep Chapter 17

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 4. Light is a form of electromagnetic energy. Explain how the effect of electric and magnetic fields on each other produces a light wave. Standardized Test Prep Chapter 17

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 4. Light is a form of electromagnetic energy. Explain how the effect of electric and magnetic fields on each other produces a light wave. Answer: The moving electric field generates a magnetic field and the moving magnetic field generates an electric field. The light wave is a combination of the two fields. Standardized Test Prep Chapter 17

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 5. Differentiate between an alternating electric current and a direct electric current. Standardized Test Prep Chapter 17

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 5. Differentiate between an alternating electric current and a direct electric current. Answer: In a direct current, the electrons always flow in one direction, but in an alternating current, the direction of flow reverses periodically. Standardized Test Prep Chapter 17

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics 7. What is the purpose of the commutator in this electric motor? F.constant direction of electron flow G.alternation of the coil magnetic field H.production of mechanical energy I.production of a magnetic field Standardized Test Prep Chapter 17

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Interpreting Graphics 7. What is the purpose of the commutator in this electric motor? F.constant direction of electron flow G.alternation of the coil magnetic field H.production of mechanical energy I.production of a magnetic field Standardized Test Prep Chapter 17