reading this section you will be able to do
how a magnetic field is created.
how the electromagnet and the solenoid work together.
In 1820, a Danish scientist named
Hans Oersted discovered that a magnetic compass could be
deflected from its resting position if a wire carrying electric
current were placed near the compass. This deflection of the compass
only occurred when current was flowing in the wire. When current
was stopped, the compass returned to its resting position.
This graphic seems to indicate that
any wire in which an electric current is flowing is surrounded
by an invisible force field called a magnetic field. For
this reason, any time we deal with current flowing in a circuit,
we must also consider the effects of this magnetic field. We have
all probably had experiences with magnets at one time or another.
Magnets attract certain types of material like iron but almost
The term electromagnetism is
defined as the production of a magnetic field by current flowing
in a conductor. We will need to understand electromagnetism in
greater detail to understand how it can be used to do work.
Coiling a current-carrying conductor
around a core material that can be easily magnetized, such as
iron, can form an electromagnet. The magnetic field will be concentrated
in the core. This arrangement is called a solenoid. The
more turns we wrap on this core, the stronger the electromagnet
and the stronger the magnetic lines of force become.
We have created an electromagnet,
which behaves just like a regular permanent bar magnet when the
current is flowing. Notice that all of the lines of force pass
through the center of the core material, regardless of how they
extend outside the coil of wire. The direction of magnetic polarity
is determined by the direction of current flowing in the coil
of wire. The direction that the wire is coiled around the core
also determines the direction of magnetic polarity. This is important
to know if we want to use the electromagnet to apply a force to
In the next sub-unit you will learn
how the electrostatic field and field intensity are related to
field is generated anytime an electrical current flows through
field around the conductor flows in closed loops.
the wire into a coil creates an electromagnet.
the wire around a piece of iron creates a solenoid.