Electromagnetism Electromagnetism

Figure 15 The electromagnets
used in salvage yards can lift
heavy scrap metal when turned
on. To put the metal back down,
the electromagnet is turned off.
464
Electromagnets
1. Tightly wrap an
insulated copper
wire around a large
iron nail, leaving 10 cm of
wire loose at each end.
2. Remove the insulation from
the ends of the wire, and
use electrical tape to
attach the ends against the
top and bottom of a D-cell.
3. Hold the end of the nail
near some paper clips,
and try to lift them up.
4. While holding the clips up
with your electromagnet,
remove the wires from the
cell.
5. Record your observations
in your ScienceLog.
Self-Check
Can you make an electromagnet
by wrapping
a coil of wire around a
wooden core? Explain
your answer.
(See page 724 to check
your answer.)
Chapter 18
Electromagnets An electromagnet is a magnet that consists
of a solenoid wrapped around an iron core. The magnetic field
produced by the solenoid causes the domains inside the iron
core to become better aligned. The magnetic field for the entire
electromagnet is the field produced by the solenoid plus the
field produced by the magnetized iron core. As a result, the
magnetic field produced by an electromagnet may be hundreds
of times stronger than the magnetic field produced by
just a solenoid with the same number of loops.
The strength of an electromagnet can be made even stronger
by increasing the number of loops in the solenoid, by increasing
the size of the iron core, and by increasing the electric
current in the wire. Some electromagnets are strong enough
to lift a car or levitate a train!
Heavy Lifting Do you remember the maglev trains discussed
at the beginning of this section? Those trains levitate because
there are strong magnets on the cars that are repelled by powerful
electromagnets in the rails. Electromagnets are particularly
useful because they can be turned on and off as needed.
Electromagnets attract objects containing iron only when a
current exists in the wire. When there is no current in the
wire, the electromagnet is turned off. Figure 15 shows an example
of how this property can be useful.
Copyright © by Holt, Rinehart and Winston. All rights reserved.