Download Section Summary - Login for National High School Learn Center

Name ____________________________ Date ____________________ Class ____________
Using Electricity and Magnetism
■
Section Summary
What Is Electromagnetism?
Key Concepts
■
How is an electric current related to a magnetic field?
■
What are some characteristics of a magnetic field produced by a current?
■
What are some characteristics of an electromagnet?
Whenever there is electricity, there is magnetism. An electric current
produces a magnetic field. This relationship between electricity and
magnetism is called electromagnetism. You cannot see electromagnetism,
but you can observe its effects. When a wire has a current, the needle of a
compass aligns with the magnetic field that the current produces. Iron filings
around a wire with a current will form a pattern that maps out the magnetic
field produced by the current.
The magnetic field produced by a current has three distinct
characteristics. The field can be turned on or off, have its direction
reversed, or have its strength changed. To turn the magnetic field on or off,
you simply turn the current on or off. To reverse the direction of the magnetic
field, you reverse the direction of the current. When the current reverses, the
magnetic field reverses also.
The magnetic field around a wire with a current forms a cylinder around
the wire. If the wire is twisted into a loop, the magnetic field becomes
stronger. The strength of the magnetic field increases as the number of loops,
or coils, increases. By winding a wire with a current into many loops you
strengthen the magnetic field in the center of the coil. A coil of wire with a
current is called a solenoid. The two ends of a solenoid act like poles. In a
solenoid, the north and south poles change with the direction of the current.
If you place a ferromagnetic material inside a solenoid, the strength of
the magnetic field increases because the ferromagnetic material becomes a
magnet. A solenoid with a ferromagnetic core is called an electromagnet.
The magnetic field of an electromagnet is produced by both the current in the
wire and the magnetized core. An electromagnet is a strong magnet that can
be turned on and off. You can increase the strength of an electromagnet is a
number of ways.
1. You can increase the current in the solenoid.
2. You can add more loops of wire to the solenoid.
3. You can wind the coils of the solenoid closer together.
4. You can use a stronger ferromagnetic material for the core.
Electromagnets are used to life heavy objects. For example, at a junkyard,
cars and other heavy metal objects can be moved by a strong electromagnet
on a crane. When the object needs to be dropped, a switch is turned off to
turn off the current and the object falls from the magnet.
© Pearson Education, Inc., publishing as Pearson Prentice Hall. All rights reserved.