Objectives

1. Section 3 Electric Currents from Magnetism Chapter 17 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.

2. Section 3 Electric Currents from Magnetism Chapter 17 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 lawstates 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.

3. Section 3 Electric Currents from Magnetism Chapter 17 Electromagnetic Induction

4. Section 3 Electric Currents from Magnetism Chapter 17 Ways of Inducing a Current in a Circuit

5. Section 3 Electric Currents from Magnetism Chapter 17 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.

6. Section 3 Electric Currents from Magnetism Chapter 17 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.

7. Section 3 Electric Currents from Magnetism Chapter 17 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 loopin an AC generator, the current produced by the generator reverses direction. • Generators produce the electrical energy you use in your home.

8. Section 3 Electric Currents from Magnetism Chapter 17 AC Generator

9. Section 3 Electric Currents from Magnetism Chapter 17 Induced Current

10. Section 3 Electric Currents from Magnetism Chapter 17 Function of a Generator

11. Section 3 Electric Currents from Magnetism Chapter 17 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)

12. Section 3 Electric Currents from Magnetism Chapter 17 Electromagnetic Wave

13. Section 3 Electric Currents from Magnetism Chapter 17 Electromagnetic Waves

14. Section 3 Electric Currents from Magnetism Chapter 17 Transformers • A transformer is a device that increases or decreases the voltage of alternating current. • Transformers can increase or decrease voltage. • The voltage induced in the secondary coil of a transformer depends on the number of loops, or turns, in the coil. • In a step-up transformer the voltage across the secondary coil is greater than the voltage across the primary coil. • In a step-down transformer, the secondary coil has fewer loops than the primary coil and the voltage is lowered by the transformer.

15. Section 3 Electric Currents from Magnetism Chapter 17 Transformers When an additional secondary circuit is added, the voltage across each is again about equal. When the primary and secondary circuits in a transformer each have one turn, the voltage across each is about equal. When the two secondary circuits are combined, the secondary circuit has about twice the voltage of the primary circuit. Actual transformers may have thousands of turns.

16. Section 3 Electric Currents from Magnetism Chapter 17 Transformer

17. Section 3 Electric Currents from Magnetism Chapter 17 Concept Mapping

18. Standardized Test Prep Chapter 17 Understanding Concepts 1. How many coil turns are needed on the secondary coil of a step-down transformer that reduces voltage from 2 400 volts to 120 volts if the primary coil has 1,000 turns? A. 1 B. 20 C. 50 D. 120

19. Standardized Test Prep Chapter 17 Understanding Concepts, continued 1. How many coil turns are needed on the secondary coil of a step-down transformer that reduces voltage from 2 400 volts to 120 volts if the primary coil has 1,000 turns? A. 1 B. 20 C. 50 D. 120

20. Standardized Test Prep Chapter 17 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.

21. Standardized Test Prep Chapter 17 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.

22. Standardized Test Prep Chapter 17 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

23. Standardized Test Prep Chapter 17 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

24. Standardized Test Prep Chapter 17 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.

25. Standardized Test Prep Chapter 17 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.

26. Standardized Test Prep Chapter 17 Understanding Concepts, continued 5. Differentiate between an alternating electric current and a direct electric current.

27. Standardized Test Prep Chapter 17 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.

28. Standardized Test Prep Chapter 17 Reading Skills A type of train that is in development uses the force of magnetism to propel it forward. It is known as a magnetic levitation or maglev train, because magnetic forces are also used to reduce friction. Instead of wheels, the train has large magnets that float above magnets in the track. Alternating electromagnetic fields drive the train forward or slow it down using magnetic attraction and repulsion. Because there is very little friction to overcome, maglev trains move rapidly while consuming less energy than traditional vehicles. 6. How does the design of the maglev train reduce friction and consume less fuel?

29. Standardized Test Prep Chapter 17 Reading Skills, continued 6. How does the design of the maglev train reduce friction and consume less fuel? Answer: Because the train "floats" on a magnetic field, there is no contact with the ground. Other kinds of railcars have wheels that turn on rails and create friction that slows the train and wastes fuel.

30. Standardized Test Prep Chapter 17 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

31. Standardized Test Prep Chapter 17 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