Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” To advance through the presentation, click the right-arrow key or the space bar. From the resources slide, click on any resource to see a presentation for that resource. From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. You may exit the slide show at any time by pressing the Esc key. How to Use This Presentation

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter Presentation Bellringers TransparenciesStandardized Test Prep Visual Concepts Resources

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetism Table of Contents Section 1 Magnets and Magnetic Fields Section 2 Magnetism from Electric Currents Section 3 Electric Currents from Magnetism Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Recognize that like magnetic poles repel and unlike poles attract. Describe the magnetic field around a permanent magnet. Explain how compasses work. Describe the orientation of Earth’s magnetic field. Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer 1.Magnets are a part of daily life. Most of us use them without thinking about it. Name five places that you use magnets. 2.If you had two bar magnets and you touched the end of one bar magnet to the end of the other bar magnet, what are the two possible outcomes? If you rotated one of the bar magnets 180°, what are the two possible outcomes? 3.Explain why a compass is a useful tool for navigation. Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer, continued 4.On Earth, there is the magnetic N pole and the geographic North Pole. According to the picture above, are they located at the same geographic location? Where do you think the magnetic S pole is located? Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnets Some materials can be made into permanent magnets. Although a magnetized piece of iron is called a “permanent” magnet, its magnetism can be weakened or even removed. Iron is a soft magnetic material. It is easily magnetized. It tends to lose its magnetic properties easily. Cobalt is a hard magnetic material. It more difficult to magnetize. Once magnetized, it doesn’t lose its magnetism easily. Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Materials Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnets, continued Magnets exert magnetic forces on each other. Like poles repel, and opposite poles attract. A magnetic pole is one of two points, such as the ends of a magnet, that have opposing magnetic qualities. Magnets have a pair of poles, a north pole and a south pole. It is impossible to isolate a south magnetic pole from a north magnetic pole. Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Poles Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Fields Magnets are sources of magnetic fields. Magnetic force is a field force. When magnets repel or attract each other, it is due to the interaction of their. A magnetic field is a region where a magnetic force can be detected. Magnetic field lines are used to represent a magnetic field. The magnetic field gets weaker with distance from the magnet. Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Fields Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Field Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Fields, continued Compasses can track magnetic fields. A compass is a magnet suspended on top of a pivot so that the magnet can rotate freely. A compass aligns with Earth’s magnetic field. Earth’s magnetic field is like that of a bar magnet. Earth’s magnetic field has changed direction throughout geologic time. Earth’s magnetic poles are not the same as its geographic poles. Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Earth’s Magnetic Field Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Earth’s Magnetic Field Section 1 Magnets and Magnetic Fields Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Describe how magnetism is produced by electric currents. Interpret the magnetic field of a solenoid and of an electromagnet. Explain the magnetic properties of a material in terms of magnetic domains. Explain how galvanometers and electric motors work. Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer The temporary magnetic field created by current flowing through a wire is used in many small appliances. 1.Make as long a list as possible of items that contain a small electric motor. 2.How can temporary electromagnets be used to turn a shaft in an electric motor? 3.A sewing machine needle can be magnetized by gently stroking it with a magnet in one direction. What is a possible explanation for this? Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer 1.List as many items as you can that use DC current. (Hint: Batteries supply DC current.) 2.List as many items as you can that use AC current. (Hint: Standard wall outlets supply AC current.) 3.If you want to plug a CD player that normally uses batteries into a wall socket, an AC adapter is required. What is the function of the AC adapter? 4.Electric power that goes into a neighborhood must be stepped down, or decreased, in voltage before it goes into a home. Explain why this is necessary. Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetism from Electric Currents Hans Christian Oersted found that magnetism is produced by moving electric charges. Electric currents produce magnetic fields. Use the right-hand rule to find the direction of the magnetic field produced by a current. The right-hand rule: If you imagine holding the wire in your right hand with your thumb pointing in the direction of the positive current, the direction your fingers would curl is in the direction of the magnetic field. Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu The Right-Hand Rule The fingertips pointing in the direction of the magnetic field. The magnetic field points counterclockwise. Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Right-Hand Rule for a Current-Carrying Wire Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Field of a Current-Carrying Wire Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetism from Electric Currents, continued The magnetic field of a coil of wire resembles that of a bar magnet. A solenoid is a coil of wire with an electric current in it. In a solenoid, the magnetic field of each loop of wire adds to the strength of the magnetic field of the loop next to it. More loops or more current can create a stronger magnetic field. An electromagnet is a coil that has a soft iron core and that acts as a magnet when an electric current is in the coil. Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Solenoid Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetism from Electric Currents, continued Magnetism can be caused by moving charges. Negatively charged electrons moving around the nuclei of all atoms make magnetic fields. Atomic nuclei also have magnetic fields because protons move within the nucleus. Each electron has a property called electron spin, which also produces a tiny magnetic field. Magnetic atoms rotate to align with the magnetic fields of nearby atoms creating small regions within the material called domains. Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Magnetic Domain Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Devices Galvanometers detect current. A galvanometer is an instrument that detects, measures, and determines the direction of a small electric current. Electric motors convert electrical energy to mechanical energy. A device called a commutator is used to make the current change direction every time the flat coil makes a half revolution. Devices called brushes connect the wires to the commutator. Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Galvanometer Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electric Motor Section 2 Magnetism from Electric Currents Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Electromagnetic Devices, continued Stereo speakers use magnetic force to produce sound. When the direction of the current in the coil of wire changes, the paper cone attached to the coil moves, producing sound waves. Section 2 Magnetism from Electric Currents Chapter 17

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

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

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

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Ways of Inducing a Current in a Circuit Section 3 Electric Currents from Magnetism Chapter 17

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

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

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

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

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

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

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

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

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

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

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Transformers When the primary and secondary circuits in a transformer each have one turn, the voltage across each is about equal. When an additional secondary circuit is added, the voltage across each is again 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. Section 3 Electric Currents from Magnetism Chapter 17

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

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

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts 1.How many coil turns are needed on the secondary coil of a step-down transformer that reduces voltage from volts to 120 volts if the primary coil has 1,000 turns? A.1 B.20 C.50 D.120 Standardized Test Prep Chapter 17

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Understanding Concepts, continued 1.How many coil turns are needed on the secondary coil of a step-down transformer that reduces voltage from volts to 120 volts if the primary coil has 1,000 turns? A.1 B.20 C.50 D.120 Standardized Test Prep Chapter 17

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

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

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

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

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

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

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

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

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter How does the design of the maglev train reduce friction and consume less fuel?

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu 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. Standardized Test Prep Chapter 17

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

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