ELECTRICITY AND MAGNETISM 22.3

Chapter Twenty-Two: Electricity and Magnetism  22.1 Properties of Magnets  22.2 Electromagnets  22.3 Electric Motors

Chapter 22.3 Learning Goals  Describe the role of electromagnetism in the function of electric motors and generators.  Contrast energy transformations in electric motors and generators.  Explain the principle of electromagnetic induction.

22.3 Electric motors and generators  Permanent magnets and electromagnets work together to make electric motors and generators.  The secret is in the ability of an electromagnet to reverse its north and south poles.

22.3 Electric motors  Around the edge of a disk are several magnets, their alternating north and south poles facing out.

22.3 Electric motors  To make the disk spin, you bring a permanent magnet close to its edge.  The free magnet attracts one of the magnets in the disk and repels the next one. The disk is a “rotor” because it rotates.

22.3 Electric motors  In a working electric motor, an electromagnet replaces the magnet you reversed with your fingers.  The electromagnet switches its poles to make the rotor keep turning.

22.3 Electric motors  As the rotor spins, a commutator reverses the direction of the current in the electromagnet.

22.3 Electric motors Motors have three parts: 1.A rotor with magnets that alternate. 2.One or more fixed magnets around the rotor. 3.A commutator that switches the direction of current to keep the rotor spinning.

22.3 Battery run electric motors  An electric motor that runs from batteries has the same three parts.  The permanent magnets are on the outside, and the electromagnets turn in the rotor.

22.3 Battery run electric motors  A simple battery powered motor has three electromagnets.

22.3 Electromagnetic induction  Motors transform electrical energy into mechanical energy.  Electric generators do the opposite.  They transform mechanical energy into electrical energy.  The process of using a moving magnet to create electric current is called electromagnetic induction.

22.3 Electromagnetic induction  A moving magnet produces a current in a coil of wire.

22.3 Generating electricity  A generator converts mechanical energy into electrical energy using the law of induction.  As long as the disk is spinning, there is a changing magnetic field through the coil and electric current is created.

Investigation 22C  Key Question: How does an electric motor work? Electromagnetic Forces

Under the Sea  Have you ever wondered what it would be like to take a “walk” on the seafloor? Engineer Jim Varnum gets to go “down under” regularly, because he is a pilot of an extremely complex robot called Jason II. This robot dives deep into the ocean and is used to take pictures and collect data from the seafloor.