Download Chapter 22 Magnetism and its Uses

Chapter 22 Magnetism and its
Uses
Objects
• 22.1 Describe the properties of magnets
• 22.1 Define the region of force around a
magnets
• 22.1 Model magnetic behavior using domains
Objects
• 22.2 Explain the magnetic effects of a current
in a wire
• 22.2 Compare and contrast ammeters and
voltmeters
• 22.2 Describe the function of an electric
motor.
Objects
• 22.3 Describe how a generator produces an
electric current using electromagnetic
induction
• 22.3 Distinguish between alternating and
direct current
• 22.3 Explain how a transformer can step up or
step down the voltage of an alternate current
Objectives
• 22.4 Describe the characteristics of
superconductors
• 22.4 Consider various applications of
superconductivity
Key Words
• Magnetism
Magnetic Pole
• Magnetic Domain Electromagnet
• Voltmeter
Magnetic Field
Ammeter
Electric Motor
• Electromagnetic Induction
• Generator
• Transformer
Direct Current
Solenoid
Alternating current
Magnetism
• Magnetism is a property of matter in which
there is a force of attraction or repulsion
between unlike or like poles
– One positive end, one negative end
• Most metals area actually NOT magnetic
– Iron, Cobalt and Nickel metals which are actually
magnetic
– Other metals can be temporary magnets
Opposites Attract
The Earth
• Earth is a big magnet.
The actual location of
the magnetic poles
change every year by
about 40 miles
• Earth’s magnetic poles
change yearly
Magnetic Declination
• Your compass points to
the magnetic pole, not to
the true north pole
• As you approach the
poles, you have to
add/subtract degrees to
go the right direction
• Compass is wrong close
to poles
• The north arrow on the
compass rose (the large
N) is pointed towards the
place on the horizon
directly beneath the
North Star! That is,
towards true north!
• And the needle (of
course) points towards
magnetic north! So the
magnetic declination for
this locality is 45 degrees
west
Magnetic Domains
• Groups of atoms with
aligned magnetic poles are
called
Magnetic Fields
• Points towards the South Pole
– So, South must be Negative end
– Since magnetic fields point towards the negative charge
• Magnetic Pole: End of magnet, strongest magnetic
field
• Earth’s North pole
– Is the south magnet
Electromagnet
• A type of magnet
created by current
passing through a coil
• Electromagnetic
Induction: The process
by which moving a wire
through a magnetic
field produces a current
Solenoid: Coils wrapped around with
a current moving through. Used in
MRI’s
Thumb points towards the North End
Magnetic Field Force
– The current causes the magnetic field
– The magnetic field in turns pushes on the wire
• Electric Motor: Turns electrical energy into
mechanical energy
Reading Current and Voltage
• Voltmeter: Determines the voltage drop
across a resistor
• Ammeters: Determine the current through a
wire
– Determined by deflection caused by the magnetic
field
Generator
• Produces electric current by rotating wires in a
magnetic field
– See simulator
Direct Current
• DC = Direct Current. The flow (current) of
electrons is in one direction
– Like a river runs only down hill, direct current only
flows one way.
– Batteries provide this type of current
Alternating Current
• AC = Alternating Current Electrons flow back
and forth. The electrons are pushed one way,
then pushed the other way.
– The electrons stay in roughly the same area, just
going back and forth. Our outlets provide this,
alternating current.
Alternating Current
– In the USA, there are three wires that transmit the
flow of energy.
• Two are at + or – 120 Volts (180 degrees out of phase)
• One is at 0 Volts
– The US has adopted a frequency of 60 Hz
• The polarity (direction of electrons) changes 120 times
per second
• Actual voltage of peaks are + and – 170 volts
Transformers
– A transformer is just a piece of iron with a pair of
wires coiled around it - one with many more turns
in the coil than the other.
– The coils of wire are not physically connected. The
iron core is immersed in an insulating oil bath
which does not conduct electricity well.
• Step Up or Step Down the Voltage
V2 N 2
Transformers

V1
N1