Transcript My Book of Electricity and Magnetism

Electricity and Magnetism
SPS10. Students will investigate the properties of
electricity and magnetism.
a. Investigate static electricity in terms of: friction,
conduction, and induction.
b. Explain the flow of electrons in terms of:
 Alternating and direct current.
 The relationship among voltage, resistance, and
current.
 Simple series and parallel circuits.
c. Investigate applications of magnetism and/or its
relationship to the movement of electrical charges as
it relates to:
• Electromagnets, simple motors, and permanent
magnets.
Electricity
Protons and Electrons
Electricity
 Everything in the world is made up of
atoms. Each atom has smaller parts in it.
One of those parts is called electrons.
Electrons can move from atom to atom.
When an electron moves to a different
atom, it causes another electron to have
to move. When electrons move quickly
from one atom to another it is called
Electricity!
Electricity (continued)
 When you talk to your friends on the telephone,
the microphone inside of the phone’s handset
changes your sound waves into electric signals.
The light shines throughout your homes when
you flip a switch. And if you stump your toe, your
nerves send signals between your brain and
muscles.
 All of these everyday occurrences are powered
by electrical pulses. A charge is a measure of the
extra positive or negative particles that an object
has.
Rules of Electric Charge
2 rules of electric charge:
1. Opposite charges attract.
2. Like charges repel.
Static Electricity
Static Electricity
Static electricity is the study of the
behavior of electric charges, including how
charge is transferred between objects.
The only reason that we are able to use
electricity in our modern world is that it is
possible to separate positive and negative
charges from each other.
Electric charge can be transferred by
friction, conduction, and induction.
Transferring Charge
Friction
Conduction
Induction
Transfer of charge
by rubbing two
different materials
together.
Transfer of charge
when two objects
come into direct
contact with each
other (touching).
Transfer of charge
without direct
contact.
Rubbing a balloon
in your hair.
Touching a metal
sphere that has
been charged by a
Van de Graff
generator.
Being struck by
lightning b/c you
are standing near
a tree.
Walking across a
carpet with socks
on.
Charging by Friction
Example 1
Example 2
Charging by Conduction
Charging by Induction
Electric Current
1.
Alternating Current
2.
Direct Current
The continuous flow of electric charge is an electric
current. There are 2 types of electric current: direct
current and alternating current.
Direct current
Flow of charges in
only one direction
Flow of charges
that regularly
reverses direction
Ohm’s Law
1. Current
2. Voltage
3. Resistance
Ohm’s Law
 Most of the electrical appliances that you use in your
homes each day are designed for 120 Volts (V).
 Light bulbs however are sold in several varieties,
from dim 40 Watt light bulbs to bright 100 Watt light
bulbs.
 These bulbs shine differently because they have
different amounts of current in them.
 The difference in their current is because of their
resistance.
 In other words, 40 W light bulbs have a
greater resistance (less current than the 100
W bulbs) and therefore give off less light.
Ohm’s Law (continued)
 You have probably noticed that electrical devices
such as video games or radios become warm after
they have been on for a long amount of time.
 As the electrons collide, with the atoms of the
material, some of their kinetic energy transfers.
 This transfer of energy causes the atoms to
vibrate, and then the material warms up.
 As the electrons are slowed by a resistor, energy
is lost in the form of heat.
 This means that current, resistance and
voltage must be linked.
Ohm’s Law (continued)
 Did you know that resistance depends on the
material used as well as the material’s length and
temperature? Longer pieces of material have greater
resistance (less current) than shorter pieces.
Calculating Resistance
 The SI unit of resistance is the ohm, Ω, which is
equal to volts per ampere.
 Resistance, R is measured in ohm’s Ω.
 Current, I is measured in amperes, A.
 Voltage, V is measured in volts, V.
Calculating Resistance (continued)
The SI unit of resistance is
the ohm, Ω, which is equal
to volts per ampere.
Voltage = Resistance x Current
• Voltage (V) is measured in volts,
V.
• Resistance ® is measured in
ohm’s Ω.
• Current (I) is measured in
amperes, A.
Practice Ohm’s Law
1. Wire A has a resistance of 2 ohms.
Wire B has a resistance of 2.5 ohms.
Both wires have the same current.
Which wire has a greater voltage?
2. What is the current in an electric field
in which voltage is 12 volts and
resistance is 1.5 ohms?
Electric Circuits
1.
Series Circuits
2.
Parallel Circuits
Electrical Circuits
 If you’ve ever seen a house being built, you
know that wires hidden inside the walls connect
to every electrical outlet and to every light
switch.
 The steady flow of electricity is called an
electric current.
 A current will move along a wire or a path
called a circuit. Circuit means to “go around.”
 There are 2 types of circuits: series circuits and
parallel circuits.
Series Circuit vs. Parallel Circuit
A series circuit is a circuit that has only
one path for the current.
A parallel circuit has two or more paths
for current to travel.
Series Circuit
Old Christmas lights were
once wired in series. If one
bulb went out, they all
went out.
Parallel Circuit
Lights in our homes are
wired in parallel circuit.
That is why we are able to
have lights on in one room,
but off in another.
Series Circuit vs. Parallel Circuits
Series
1.
Parallel
1. Has two or more paths
Has a single loop for
for electrons to flow
electrons to travel around
through
2. Components are
connected one after
another
3. Current has to travel
through all components
2. Current is shared
between the branches
Circuit Symbols
Guards/Safety Devices Against
Overheating
 An electric fuse contains a small piece of metal
that melts if the current becomes too high,
opening the circuit and stopping the flow of
current.
 A circuit breaker contains a small piece of metal
that bends when it gets hot, opening the circuit
and stopping the flow of current.
Magnetism
The History of Magnets
 Magnetism is the force of attraction or repulsion of a
magnetic material due to the arrangement of its atoms,
particularly its electrons.
 Magnets have been known for centuries. The Chinese
and Greeks knew about the “magical” properties of
magnets. The ancient Greeks used a stone substance
called “magnetite.” They discovered that the stone
always pointed in the same direction. Later, stones of
magnetite called “lodestones” were used in navigation.
Magnetic Poles
Like Poles: Repel
 The ends of a magnet are
where the magnetic effect is
the strongest. These are
called “poles.” Each magnet
has
 2 poles: 1 North & 1 South.
 If you cut a magnet in half,
you get two magnets.
Opposite poles: Attract
Permanent Magnets vs.
Temporary Magnets
 Some magnets occur in nature. These magnets are
called natural magnets. Natural magnets maintain their
magnetic properties and therefore are permanent
magnets. (ex. lodestone).
 Some materials that are not natural magnets are easy to
magnetize (ex. Iron). A material that is easily
magnetized tends to lose its magnetism quickly, and is
called a temporary magnet.
Electromagnetic
 An electric current passing through a wire causes a
magnetic field.
 An electromagnet is a temporary magnet made by
wrapping a current-carrying wire around an iron core.
 The center of an electromagnet is called the core, and it
is often made of iron.
 As long as current is flowing, an electromagnet has a
magnetic field.
 When current is turned off, there is no longer a magnetic
field.
Electromagnets
 There are two ways to make an electromagnet
stronger:
1. increasing the number of coils
2. increasing the amount of current
 Electromagnets are useful because they can be
turned on and off. Electromagnets have many
important uses:
 ex. radios, telephones, computers
Electric Motors vs. Generators
 An electric motor is a device that changes electrical
energy into mechanical energy.
 An electric motor is made up of an electromagnet and a
permanent magnet.
 So, what do windshield wipers, CD players, VCR's,
blenders, ice makers, computers, and talking toys all
have in common? They all contain electric motors!
Electric Motors vs. Generators
 A generator is a device that changes mechanical energy
into electrical energy.
 Most of the energy we use every day comes from
generators.
 Mechanical energy for many generators is supplied by
turbines.
 A turbine is a large wheel that is turned by moving
steam or water.
Electric Motors vs. Generators
Motor or Generator?
Motor or Generator?