UNIT FIVE: Electricity and Magnetism • Chapter 16 Electricity • Chapter 17 Magnetism
Chapter Seventeen: Magnetism • 17.1 Properties of Magnets • 17.2 Electromagnets • 17.3 Electric Motors and Generators • 17.4 Generating Electricity
Chapter 17.2 Learning Goals • Define electromagnet. • Build a simple electromagnet. • Compare permanent magnets and electromagnets.
Key Question: How are electricity and magnetism related? Investigation 17B Electromagnets
17.2 Electomagnets • Electromagnets are magnets that are created when there is electric current flowing in a wire. • The simplest electromagnet uses a coil of wire wrapped around some iron.
17.2 Right hand rule • To find the north pole of an electromagnet, use the right hand rule. • When the fingers of your right hand curl in the direction of the wire, your thumb points toward the magnet’s north pole.
17.2 Electromagnets in Toasters • By changing the amount of current, you can easily change the strength of an electromagnet or even turn its magnetism on and off. A toaster tray is pulled down by an electromagnet while bread is toasting.
17.2 Doorbells • A doorbell contains an electromagnet. • When the button of the bell is pushed, it sends current through the electromagnet.
17.2 Building an electromagnet • You can easily build an electromagnet from wire and a piece of iron, such as a nail. • Wrap the wire in many turns around the nail and connect a battery.
17.2 Building an electromagnet • There are two ways to increase the current in a simple electromagnet: • Apply more voltage by adding a second battery. • Add more turns of wire around the nail. Why do these two techniques work?
17.2 Similarities in permanent and electromagnets • The charged electrons in atoms behave like small loops of current. • Electric current through loops of wire creates an electromagnet. • Atomic-scale electric currents create a permanent magnet.
17.2 Magnetic materials • Atoms act like tiny magnets. Permanent magnets have their atoms aligned, creating the magnetic forces we observe.
17.2 Magnetic materials • In iron, the atoms are free to rotate and easily align their individual north and south poles.
17.2 Nonmagnetic materials • The atoms in non-magnetic materials, like plastic, are not free to move or change their magnetic orientation.