Transcript Unit 6 Magnetism

Unit 6
Magnetism
Chapter 8
Pages 226-255
Magnets
• Two magnets exert a force on each other
• The magnetic force is the interaction you feel
before the two magnets even touch each
other
• The strength of this force increases as you
move the magnets closer together
• The magnetic field exerts the magnetic force
• Each magnet has a north and south pole
• This is where the magnetic force is the
strongest
• Like poles repel
• Opposite poles attract
Earth’s Magnetic Field
• On a compass, the needle points to
geographic North
• This is because earth’s south magnetic pole is
located in Canada
• So opposites attract
• The north on the compass to the “south” in
Canada
Magnetic Domains
• Groups of atoms with aligned magnetic poles
are called magnetic domains
• This allows the object to behave like a
magnetic with a north and south pole
• Ex: Placing a magnet against an iron nail will
cause all the atoms to orient themselves in
the same direction and temporarily cause the
nail to act as a magnet
Electric Current and Magnetism
• Moving charges produce magnetic fields
• The direction of the field depends on the
direction of the current
• The strength of the field depends on the
amount of current flowing through the wire
Electromagnets
• An electromagnet is a temporary magnet made
by placing iron inside a current carrying coil of
wire
• The more the wire is coiled around the iron, it
causes a stronger magnetic field
• When current flows through the electromagnet it
moves toward or away from another magnet,
converting electric energy into mechanical energy
to do work
• Ex: stereo speakers contain electromagnets
Galvanometers
• Gauges are your dashboard of your car are
galvanometers
• They measure the current being sent from
sensors which in turn register the amount of
ex: gasoline you have left
Electric Motors
• An electric motor is a device that changes
electrical energy into mechanical energy
• Like galvanometers, electric motors use an
electromagnet
• The movement of the current is constantly
switched back and forth to maintain the
rotation of the coil
• Some motors use a commutator to do this,
others use household alternating current
• Electric motors are most useful if their
rotation speed is controlled
• Today’s motors are smaller, more powerful,
and more efficient than the first ones
developed in the late 1800s
Electric Generators
• Electromagnetic induction is caused when a
magnetic is moved through a wire coil or
rotating a coil of wire through a magnetic field
• This is how generators produce electricity
• Again, the current flow must constantly switch
directions in order for the coil to turn
continuously
Types of Generators
• In your car, it is called an alternator
• Power plants use generators to allow
electricity to reach your home
• Here the electromagnets are connected to a
turbine pushed by either water, wind, or
steam
Direct and Alternating Currents
• A battery produces a direct current, which
flows in only one direction of a wire
• Generators produce alternating current, which
reverses the direction of current flow in a
regular way
Transformers
• Alternating current traveling through power
lines is a high voltage so as to reduce the
amount of energy lost as heat
• A transformer can either decrease the voltage
(step down) or increase it (step up)
• Step up transformers have more turns of wire
in the secondary coil than in the primary coil