Transcript NOTES 18 – Magnetism & Electricity What is a magnet? • Magnet – an object that produces a magnetic field which can apply.

NOTES 18 – Magnetism &
Electricity
What is a magnet?
• Magnet – an object that produces a magnetic
field which can apply force to another object
• Some objects can be magnetized and are
called permanent magnets (EX. An iron bar)
• Magnetic Field – An area around a magnet
where a magnetic force can be detected
• Can push or pull on other magnetic objects
causing them to move – In other words, they
can apply a force over a distance to move an
object (Do work)
Earth Has a Magnetic Field
• Earth’s magnetic field extends into space
• It protects us from radioactive particles
Some particles get through at the
poles creating the auroras
Aurora Borealis
charged particles affected
by the Earth’s magnetic field
Magnets Have Two Poles
• All magnetic objects have
two poles which we call
north and south (N and
S)
• Like poles repel each
other
• N  N
S  S
• Opposite poles attract
each other
• N  S
Magnetism & Electricity Are Related
• All magnetism is produced by moving electric
charges
• A current-carrying wire produces a magnetic
field
• Solenoid – a coil of wire with current running
through it
• More current = stronger magnetic field
• More coils = stronger magnetic field
• Electromagnet – a solenoid where the coil of
wire is wrapped around an iron core (stronger
than a solenoid)
Uses of Electromagnets
• Electric Motor – device that uses magnetism to
convert electrical energy into mechanical energy
• When current is running through the coil of
wire, an electromagnet between permanent
magnets is repelled and spins
• The spinning electromagnet can be attached
to a shaft so it can do work
• The shaft is connected to some other device,
like a propeller or a wheel
• EX. Fans, Electric Drills, Computer Hard
Drives
Uses of Electromagnets
• Speakers
• Current flowing through
an electromagnet
constantly changes
direction
• The electromagnet
alternates between
attracting and repelling
a permanent magnet
• This moves the
speaker cone back and
forth producing sound
Magnetism Can Produce Electric Current
• Electromagnetic Induction – making
current flow in a circuit by moving a
magnetic field
• Faraday’s Law – An electric current can
be produced in a circuit by a moving
magnetic field
• Current is also produced when wire is
moved through a magnetic field
Using Generators to Produce Electricity
• Generator – a machine that
converts mechanical energy into
electrical energy
• Loops of wire are turned
quickly in a magnetic field
• Current is induced in the wire
and flows out of the
generator
• Current changes direction
every half turn of the
generator – this is called
alternating current or AC
Generators Do Not Create Energy
• Generators obey the Law of Conservation of
Energy
• Some other form of energy must be used to
make the generator spin
• The energy to turn generators in power plants
comes from a variety of sources:
• Burning coal (most common, dirty)
• Falling water (hydroelectric, geographically
limited)
• Nuclear (produces radioactive waste)
• Wind/Solar/Geothermal (expensive, limited)
Transformers Can Increase or
Decrease Voltage
• Transformer – a device that increases or
decreases the voltage of alternating current
• Step-up Transformer – increases voltage
• Step-down Transformer – decreases voltage
• EX. A step-up transformer is used near the
power plant to increase voltage to about
120,000 V and a step-down transformer is used
near your home to decrease the voltage to about
120 V, which is much safer