Chapter 2
Section 1
Electromagnetism
Magnets and magnetism
Vocabulary:
magnet –
magnetic pole –
magnetic force –
Notes
Properties of Magnets
Magnetic Poles – on a magnet, the magnetic poles are the locations where the magnetic forces
are the strongest.
North and South - the poles of a magnet will always face away from each other; there will
always be two poles on a magnet.
Magnetic Forces – these are the forces due to charges moving inside of the magnet; opposite
poles will attract each other (South & North) and like poles will repel each other (North &
North).
Magnetic Fields – this is the area around a magnet where the magnetic forces interact with
other objects. This region can be visualized with field lines drawn from one end of the bar
magnet to the other – the closer the lines are together , the stronger the force.
On the figure below draw the field lines and label the poles.
The Cause of Magnetism
Atoms and Domains – all matter is made of atoms that have electrons which make a magnetic
field. Each of these atoms make up larger regions called domains that all act like tiny magnets
within the substance. These domains determine if the material is magnetic or not.
Losing Alignment – there are a variety of ways to de-magnetize a substance: one way is to
increase the temperature; dropping the magnet really hard; & putting the magnet in another,
stronger magnetic field, opposite of its own.
Making Magnets – using materials that can be magnetized (iron, nickel, & cobalt), the domains
need to be aligned using another magnetic field, and this will cause your object to become
magnetized.
Cutting Magnets – when you cut a magnet into smaller pieces, you will still have a magnet
with two poles.
Kinds of Magnets
Temporary & Permanent Magnets – the difference between the two magnets is that
permanent magnets require more effort to magnetize, but will hold their magnetism longer
than temporary magnets which are easier to magnetize.
Earth as a Magnet
One Giant Magnet – the Earth acts like one giant magnet, as if there is a large bar magnet
running through it.
Poles of a Compass Needle – the compass needle is a small magnet that will point to the
magnetic poles of Earth.
South Magnetic Pole near North Geographic Pole – the north pole of compass needle points
North to a magnetic south pole
The Core of the Matter – the magnetic north and south poles are created by the movement of
electric charges in the Earth’s core as the liquid core moves around.
A Magnetic Light Show – auroras are caused by the interaction of charged particles (ions) from
the sun hitting the gases in the Earth’s atmosphere, which create a spectacular light show in
the night sky near the magnetic poles.
Section 2
Magnetism from Electricity
Vocabulary
electromagnetism –
solenoid –
electromagnets –
electric motor –
Notes
The Discovery of Electromagnetism – Oersted found that there was a direct relationship between
electricity and magnetism.
More Research – the direction of the electric current will determine the direction of the
magnetic field.
Using Electromagnets
Solenoids – this is a coil of wire that carries an electric current to produce a magnetic field
similar to a bar magnet. The strength of a solenoid is determined by the number of loops in
the wire and the amount of current in the wire as well.
Electromagnets – this solenoid that has an iron core (or other similar metal) within the loops;
this is a coil of wires that are wrapped around a core and has electricity moving through the
wire.
Turning Electromagnets On & Off – controlling an electromagnet is as simple as controlling the
electricity flowing through the wires. When there is no electricity the electromagnet is off and
when the electricity is on, the electromagnet will be magnetized.
Applications of Electromagnetism
-
There are many different applications for electromagnets.
Doorbells – these use two solenoids to ring bell bars in the doorbell when the button is
pushed.
Magnetic Force and Electric Current – when a magnetic field is brought near a current carrying
wire, the wire will jump or move based on the magnetic field and current in the wire.
Electric Motors – these are devices that use an electric current, a wire loop (armature), and a
permanent magnet to convert electrical energy to mechanical energy.
Galvanometers – a device that uses an electromagnet and a permanent magnet to measure
either electric voltage or electric current.
Section 3
Electricity from Magnetism
Vocabulary
electromagnetic induction –
electric generator –
transformer –
Notes
Electric Current from a Changing Magnetic Field – Oersted discovered that electric current can
make a magnetic field. It was not until the work of Michael Faraday and Joseph Henry that
electricity could be made by a magnetic field.
Faraday’s Experiment –His initial experiment to make electric current using an electromagnet
was not successful at first.
Success for an Instant – Electric current was created only when the magnetic field was
changing (when the current was changing). Process called electromagnetic induction.
Inducing Electric Current – Faraday’s experiment also showed that moving a magnet or wire
through an electromagnetic field causes an electric current to flow through the wire.
Electric Generators
-
These devices use the principles of electromagnetic induction to create an
electrical current.
Alternating Current – this is a current that is produced because of the differences in the
magnetic fields of a generator. Alternating current moves in two directions, not one like direct
current.
Generating Electric Energy – the process of electrical energy production comes from nuclear
reactions, hydroelectric power, wind turbines, geothermal, solar panels, and the burning of
fuels like coal and gas to create steam to drive the turbines.
Transformers
-
These are devices that use coils of wire and iron rings to electromagnetically
induce a current in another coil of wires to change the voltage and current in a
series of wires.
Step-up; Step-down – In a step up transformer the voltage will increase in the wires, while the
current will decrease – all the while keeping electrical power the same. In a step down
transformer the voltage will decrease and the current will increase.
Step-up: Number of loops is greater on the secondary coil.
Step-down: Number of loops is greater in the primary coil.
Electrical Energy for Your Home – the energy that comes to your home has gone through 2-3
different transformations after leaving the power plant.