Electromagnetism

1. Electromagnetism Preview Section 1 Magnets and Magnetism Section 2 Magnetism from Electricity Section 3 Electricity from Magnetism Concept Mapping

2. Section1 Magnets and Magnetism Bellringer Given the following objects, a piece of aluminum foil, a nickel, a plastic figure, a piece of wood, a glass vase, and some paper clips, predict which objects will be attracted to a magnet. How do you know? Record your answers in your science journal.

3. Section1 Magnets and Magnetism Objectives • Describe the properties of magnets. • Explain why some materials are magnetic and some are not. • Describe four kinds of magnets. • Give two examples of the effect of Earth’s magnetic field.

4. Section1 Magnets and Magnetism Properties of Magnets • Magnetic Polesare points on a magnet that have opposite magnetic qualities. • North and SouthThe pole of a magnet that points to the north is called the magnet’s north pole. The opposite end of the magnet, called the south pole, points to the south.

5. Section1 Magnets and Magnetism Properties of Magnets, continued • Magnetic Forces When you bring two magnets close together, the magnets each exert a magneticforce on the other. These magnetic forces result from spinning electric charges in the magnets. The force can either push the magnets apart of pull them together.

6. Section1 Magnets and Magnetism

7. Section1 Magnets and Magnetism Properties of Magnets, continued • Magnetic FieldsA magnetic field exists in the region around a magnet in which magnetic forces can act.

8. Section1 Magnets and Magnetism The Cause of Magnetism • Atoms and DomainsIn materials such as iron, nickel, and cobalt, groups of atoms are in tiny areas called domains. The north and south poles of the atoms in a domain line up and make a strong magnetic field.

9. Section1 Magnets and Magnetism The Cause of Magnetism, continued • Losing AlignmentWhen domains move, the magnet is demagnetized, or loses its magnetic properties. • Making MagnetsYou can make a magnet from demagnetized material if you line up its domains with another magnet.

10. Section1 Magnets and Magnetism The Cause of Magnetism, continued • Cutting a MagnetWhen you cut a magnet in half, you end up with two magnets.

11. Section1 Magnets and Magnetism Kinds of Magnets • Atoms and DomainsSome magnets, called ferromagnets, are made of iron, nickel, cobalt, or mixtures of those metals. Another kind of magnet is the electromagnet. This is a magnet made by an electric current. • Temporary and Permanent MagnetsTemporary magnets are made from materials that are easy to magnetize. But they tend to lose their magnetization easily. Permanent magnets are difficult to magnetize, but tend to keep their magnetic properties longer.

12. Section1 Magnets and Magnetism Earth as a Magnet • One Giant MagnetEarth behaves as if it has a bar magnet running through its center. • Poles of a Compass NeedleThe point of a compass needle is attracted to the south pole of a magnet. Opposite poles of magnets attract each other. • South Magnetic Pole near North Geographic PoleA compass needle points north because the magnetic pole of Earth that is closest to the geographic North Pole is a magnetic south pole.

13. Section1 Magnets and Magnetism

14. Section1 Magnets and Magnetism Earth as a Magnet, continued • The Core of the MatterScientists think that the Earth’s magnetic field is made by the movement of electric charges in the Earth’s core. • A Magnetic Light ShowEarth’s magnetic field plays a part in making auroras. An aurora is formed when charged particles from the sun hit oxygen and nitrogen atoms in the air.

15. Section1 Magnets and Magnetism Earth’s Magnetic Field Click below to watch the Visual Concept. Visual Concept

16. Section2 Magnetism from Electricity Bellringer Suppose you had a machine that could levitate heavy objects with the flick of a switch. Write a paragraph in yourscience journalabout how this machine would make your life easier.

17. Section2 Magnetism from Electricity Objectives • Identify the relationship between an electric current and a magnetic field. • Compare solenoids and electromagnets. • Describe how electromagnetism is involved in the operation of doorbells, electric motors, and galvanometers.

18. Section2 Magnetism from Electricity The Discovery of Electromagnetism • Hans Christian Oersted Danish physicist Hans Christian Oersted discovered the relationship between electricity and magnetism in 1820. • More ResearchFrom his experiments, Oersted concluded that an electric current produces a magnetic field. His research was the first research in electromagnetism—the interaction between electricity and magnetism.

19. Section2 Magnetism from Electricity

20. Section2 Magnetism from Electricity Using Electromagnetism • Asolenoidis a coil of wire that produces a magnetic field when carrying an electric current. • An electromagnet is made up of a solenoid wrapped around an iron core. • Turning Electromagnets On and OffElectromagnets are very useful because they can be turned on and off as needed. The solenoid has a field only when there is electric current in it.

21. Section2 Magnetism from Electricity Applications of Electromagnetism • DoorbellsTwo solenoids in a doorbell allow the doorbell to work. • Magnetic Force and Electric CurrentAn electric current can cause a compass needle to move. The needle is a small magnet. This property is useful in electric motors.

22. Section2 Magnetism from Electricity Applications of Electromagnetism, continued • An electric motoris a device that changes electrical energy into mechanical energy.All electric motors have an armature—a loop or coil of wire that can rotate. • GalvanometersA galvanometer measures current. A galvanometer has an electromagnet placed between the poles of a permanent magnet.

23. Section2 Magnetism from Electricity

24. Section3 Electricity from Magnetism Bellringer Have you ever discovered something by accident? Maybe you looked in a dictionary for the definition of an unknown word, only to find the definition of another word you didn’t know. Write a short paragraph in your science journaldescribing how you have discovered something by accident.

25. Section3 Electricity from Magnetism Objectives • Explain how a magnetic field can make an electric current. • Explain how electromagnetic induction is used in a generator. • Compare step-up and step-down transformers.

26. Section3 Electricity from Magnetism Electric Current from a Changing Magnetic Field • Faraday’s Experiment Michael Faraday conducted an experiment trying to get the magnetic field of the electromagnet to make an electric current in a second wire.

27. Section3 Electricity from Magnetism Electric Current from a Changing Magnetic Field, continued • Success for an InstantFaraday realized that electric current in the second wire was made only when the magnetic field was changing. The process by which an electric current is made by changing a magnetic field is called electromagnetic induction. • Inducing Electric CurrentLook at the next slide to see electromagnetic induction.

28. Section3 Electricity from Magnetism

29. Section3 Electricity from Magnetism Electric Generators • Alternating Current The electric current produced by the generator shown on the next slidechanges direction each time the coil makes a half turn. Because the electric current changes direction, it is an alternating current. • Generating Electrical EnergyThe energy that generators convert into electrical energy comes from different sources such as fossil fuels and nuclear energy.

30. Section3 Electricity from Magnetism

31. Section3 Electricity from Magnetism Transformers • A transformer increases or decreases the voltage of alternating current. • Step Up, Step Down The number of loops in the primary and secondary coils of a transformer determines whether it increases or decreases the voltage. • Electrical Energy for Your HomeThe electric current that brings electrical energy to your home is usually transformed three times.

32. Section3 Electricity from Magnetism Transformers, continued

33. Electromagnetism Concept Mapping Use the terms below to complete the concept map on the next slide. mechanical energy electrical energy electromagnetic induction electric motor transformers voltage

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