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Section 1: Magnets and Magnetic Fields
Section 2: Magnetism from Electric Currents
Section 3: Electric Currents from Magnetism
Key Terms
Magnetic Poles
Magnetic Fields
Magnets
The name magnet comes from the region of
Magnesia which now modern day Greece
The first magnetic rocks called Lodestones
were found in this region almost 3000 yrs
ago.
A lodestone is composed of an iron-based
material called magnetite
Some materials can be made into permanent
magnets
Some materials like lodestones are always
magnetic. These materials are called
permanent magnets.
However, some materials like iron can become
permanent magnets
By rubbing a permanent magnet against a
piece of iron, the iron will become permanent
magnetic.
A slower process in producing a permanent
magnet from a piece of iron would be placing
the iron near a strong magnet.
Creating a permanent magnet from a piece of
iron does not mean the iron will always be
magnetic
The magnetism of the iron can be weakened or
completely removed. This can be accomplished
by heating or hammering the piece of iron.
Magnetically Soft – a material that is easily
magnetized but also loses its magnetism easily.
(Iron)
Magnetically Hard – a material that is hard to
magnetize and does not lose their magnetism
easily. ( Cobalt and Nickel)
Magnets exert magnetic forces on each other
Like poles repel, and opposite poles attract
Magnets have a pair of poles, the north pole
and south pole.
It is impossible to isolate a magnetic pole. If
you cut a magnet in half it will still have a
north and south pole. NO MATTER HOW
SMALL
Magnetic Fields
If two like poles are brought close together and
one magnet is free to move, the closer you
bring the poles the free moving magnet will
start to move away.
Magnets are sources of magnetic fields
Magnetic force is a field force. When magnets
repel or attract each other, it is due to the
interaction of their magnetic fields.
The strength of a magnetic field depends on
what the magnet is made of and the degree
to which it has been magnetized
Magnetic field lines are used to show magnetic
fields
The magnetic field gets weaker with distance.
The further apart magnetic field lines are
represents a weak field. The closer together,
the stronger the field
Magnetic fields are strongest at the poles
Compasses can track magnetic fields. A
compass is a magnet suspended on top of a
pivot so that the magnet can rotate freely
A compass aligns with Earth’s magnetic field.
The first compasses were made from
lodestones.
Earth’s magnetic field is like that of a bar
magnet
Earth’s magnetic poles are not the same as its
geographic poles
The magnetic pole in Antarctica is actually a
magnetic N pole, and the magnetic pole in
northern Canada is actually a magnetic S
pole.
Key Terms
Solenoid
Electromagnet
Galvanometer
Electric Motor
Magnetism from Electric Currents
In 1820 a Danish science teacher named
Hans Christian Oersted first experimented
with the effects of an electric current on
the needle of a compass
Electric currents produce magnetic fields
Use the right-hand rule to finde the direction
of the magnetic field produced by a current
If you imagine holding the wire in your right hand with your
thumb pointing in the direction of the positive current, the
direction your fingers would curl is in the direction of the
magnetic field.
The magnetic field of a coil of wire resembles
that of a bar magnet
By wrapping a wire in to a coil you can increase
the magnetic field without increasing a fire
hazard.
A coil of wire with an electric current is called a
solenoid
A solenoid will have a north and a south pole
just like a magnet
The strength of the magnetic field in a solenoid
depends on the number of coils or the
amount of current in the wire. By increasing
the number of coils or the amount of current
you can increase the strength of the magnet.
Another way to increase the magnetic field of a
solenoid is to place a magnetic material in the
center of the coil
By placing a magnetic material in the center of
a solenoid, an electromagnet is created.
Magnetism can be caused by moving charges
Negatively charged electrons moving around
the nuclei of all atoms make magnetic fields.
Nuclei also have magnetism because of proton
movement.
Each electron with in an atom has a property
called electron spin, which also produce
magnetic fields
When a potentially magnetic substance is not
magnetized, its domains are randomly
oriented
When the domains become more uniform the
substance becomes magnetized
Electromagnetic Devices
Galvanometer detect current
Galvanometers are devices used to measure
current in ammeters and voltage in voltmeters.
A galvanometer consists of a coil of insulated wire
wrapped around an iron core that can rotate
between the poles of a permanent magnet
Electric motors convert electrical energy to
mechanical energy
A device called a commutator is used to make
the current change direction every time the
flat coil makes a half revolution.
Devices called brushes connect the wires to the
commutator.
Stereo speakers use magnetic force to produce
sound
In a speaker, when the direction of the current
in the coil of wire changes, the paper cone
attached to the coil moves, producing sound
waves.
Key Terms
Electromagnetic Induction
Generator
Alternating Current
Transformer
In 1831, Michael Faraday discovered that a
current can be produced by pushing a
magnet through a coil or wire
Electromagnetic induction is the process of
creating a current in a circuit by changing a
magnetic field
Electromagnetic induction and Faraday’s Law
Faraday’s Law states that an electric current
can be produced in a circuit by a changing
magnetic field.
It may seem that electromagnetic induction is
created from nothing, but it does not violate
the law of conservation of energy.
An outside source is needed to move a loop
through the magnetic field.
Moving electric charges experience a magnetic
force when in a magnetic field
The force is at its maximum value when the
charge moves perpendicular to the magnetic
field.
When the wire in a circuit moves perpendicular
to a magnetic field, the current induced in the
wire is at a maximum
When the wire moves parallel to a magnetic
field, there is zero current induced in the wire
Generators convert mechanical energy to
electrical energy
Alternating currents are electric currents that
change direction at regular intervals (AC)
In an alternating current generator, the
mechanical energy of the loop’s rotation is
converted to electrical energy when a current
is induced in the wire.
Table 1 pg 579
Generators produce the electrical energy you
use in your home
The mechanical energy used in a commercial
power plant comes from a variety of sources.
Dams
Coal
Nuclear Fission
Hot Water
Solar Power
Wind
Electricity and magnetism are two aspects of a
single electromagnetic force
Light is a from of electromagnetic energy.
Visible light travels as electromagnetic waves
or EM waves, as to other forms of radiation
(X rays and radio signals) called EMF
electromagnetic frequency waves
EM waves are made up of oscillating electric
and magnetic fields that are perpendicular to
each other
EM waves are transverse waves
Transformers
Transformers are devices that increase or
decrease the voltage of alternating current
Two wires are coiled around opposite sides of
a closed iron loop. One wire is attached to a
source of alternating current, such as a power
outlet. The other wire is attached to an
appliance.
Transformers can increase or decrease voltage
The voltage induced in the secondary coil of a
transformer depends on the number of loops,
or turns in the coil
When the primary and secondary circuits in a
transformer each have one turn, the voltage
across each is about equal.
When an additional secondary circuit is added,
the voltage across each is again about equal
When the two secondary circuits are combined,
the secondary circuit has about twice the
voltage of the primary circuit. Actual
transformers may have thousands of turns.
When the secondary coil produces a higher
voltage than the primary coil this is a step-up
transformer.
If the voltage on the primary coil is greater
than the voltage on the secondary coil this is
a step-down transformer. (Transformers of
power lines)
A step-up transformer is used at or near the
power plant to increase the voltage of the
current to about 120,000 V.
A step-down transformer is use near homes to
reduce the voltage to around 120 V.