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 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 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 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 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