Download Electricity and Magnetism - Unit 1

Electricity and
Magnetism
Unit 4
Electricity
S8P5: Students will recognize characteristics
of gravity, electricity, and magnetism as major
forces acting in nature.
B. Students will demonstrate the advantages
and disadvantages of series and parallel
circuits and how they transfer energy.
Electric Charge
All matter is made up of very small
particles called atoms.
 What are the 2 types of charged
particles in atoms?
 1. Protons- positively charged
particles
 2. Electrons- negatively charged
particles

Parts of an Atom

PROTONS
 Each element on the
Periodic Table has a
different number of
protons.
• Protons have a
positive charge
• Found within the
nucleus of the atom
• Change the number
of protons 
change element
p
Parts of an Atom

ELECTRONS
 An element on the
Periodic Table has the
same number of
electrons and protons.
• Electrons have a
negative charge
• Found outside the
nucleus in the
electron clouds
• Change the number
of electrons  ionize
the element (give it a
charge)
e
-
Parts of an Atom
n

NEUTRONS
 Most elements also
have neutrons
(except for
Hydrogen)
• Neutrons have
no charge
(neutral)
• Found in the
nucleus of the
atom
The Law of Electric
Charges

Law of Electric Charges: like charges
repel and opposite charges attract
Charges
 Like
charges repel
Charges
 Opposite
charges attract
Electric Force and Electric
Field
Electric Force: the force of attraction
or repulsion on a charged particle
that is due to an electric field
 The greater the amount of charge,
the greater the electric force.
 The closer the charges are, the
greater the electric force.
 Electric Field: the space around a
charged object in which another
charged object experiences an
electric force

Three Ways to Charge an
Object

Friction: Charging by friction happens when
electrons are “wiped” from one object onto
another.

Conduction: Charging by conduction happens
when electrons move from one object to another
by direct contact.

Induction: Charging by induction happens when
charges in an uncharged object are rearranged
without direct contact with a charged object.
Electrical Potential Energy
 Electrical
charges can be stored
on or in objects as potential
energy.
 Examples:
 Electricity in a battery
 Rubbing your socks on carpet
 Electricity in clouds
Static Electricity


Static Electricity
 the accumulation of electric charges
on an object that are at rest
 generally produced by friction or
induction
 When something is static, it is not
moving.
3 examples of Static Electricity
 Clothes from a dryer sticking together
 Balloon sticking to clothes after
rubbing it on your hair
 Negative charges on the bottom of a
cloud during a thunderstorm
Electric Discharge


Electric discharge:
the release of static
electricity as charges
move off an object
2 examples of
electric discharge:
 1. Walking across
carpet and
touching a metal
doorknob
 2. Lightning
Electrical Kinetic Energy

Electricity
 electrical energy due to the flow of electrons

Electric current
 the rate at which electric charges pass through a
given point (the rate that electrons flow)

The greater the flow of charge, the higher the current.

Electrons move from negative to positive.
Electric charges will always flow from a region of
higher potential energy to a region of lower potential
energy.
 The difference in potential energy between two
locations is known as potential difference (voltage).

Electrical Conductors
 Electrical
conductor:
 a material in which electrons
can move through easily
 Electrons (e-) are loosely
held
 Examples: Most metals
(copper, aluminum, and
mercury)
Electrical Insulators

Electrical insulator
 a material in which electrons are not
able to move easily
 Electrons (e-) are tightly held
 Examples: Plastic, rubber, glass, wood,
and air
DC and AC



2 types of electric
currents:
 DC: direct current
 AC: alternating
current
In a direct current, the
charges always flow in
the same direction (one
way).
 Ex. Dry cell battery
In an alternating
current, the charges
continually shift from
flowing in one direction
to the reverse direction
at regular intervals (two
ways).
Voltage

Voltage
 the push or force that
causes electrons to move
from negative to positive
 a measure of how much
work is needed to move a
charge between two points
• The size of the current
depends on the voltage.
• The greater the voltage, the
greater the current.
• A greater current means that
more charges move in the wire
each second.
Resistance





Resistance
 a measure of how difficult it is
for electrons to move through
a material
 electrical energy is converted
to thermal energy and light
(Ex.: a light bulb)
You can think of resistance as
Copper - low resistance
“electrical friction.”
A resistor is an object that is
added to a circuit that restricts
the flow of electrical energy.
An object’s resistance depends
on its material, thickness, length,
and temperature.
Good conductors, such as
copper, have a low
resistance. However, poor
conductors, such as
Tungsten, have a higher
resistance.
Tungsten - high resistan
Cells




Batteries are chemical cells.
Batteries convert chemical
energy into electricity.
A battery can provide the
voltage (push) that is needed
to keep current flowing in a
circuit.
• Electric charges are
repelled by the negative
terminal and attracted
toward the positive
terminal.
Photocells are devices that
convert light energy into
electrical energy.
 Ex. Solar panels
Electric Circuits:
Parts of an Electric Circuit

What is a circuit?
-a complete, closed path through which electric charges flow

Just like a roller coaster, an electric circuit forms a loop; it begins
and ends in the same place.

All circuits need 3 basic parts.
1. Energy source- provides energy to the circuit; can be a
battery, a photocell, or an electric generator at a power plant
2. Wires- connect the other parts of a circuit; made of conducting
materials that have low resistance, such as copper
3. Loads- change electrical energy into other forms of energy;
examples include light bulbs, appliances, televisions, and electric
motors
A Switch to Control a
Circuit



A switch is used to open and close a circuit.
In order for loads (like the lights in this classroom) to work, the
switch needs to be closed to allow charges to flow through.
If a switch is open, the load will not work.
Types of Circuits

What are the 2
types of circuits?
 Series circuits
 Parallel circuits
Series Circuit

Series Circuit:
 a circuit in which all the parts are connected in a single loop
 only one (single) path for charges to follow; so, the charges
moving through this circuit must flow through each part of the
circuit.


Series Circuits:
Advantages and
Disadvantages
Advantages:
 The bulbs and batteries will last longer.
 Use less power
 The current is the same throughout the circuit; therefore,
lights shine with equal brightness.
Disadvantages
 Lights get dimmer as more lights are added.
• Each device (light bulb, etc.) receives a fraction of the
total voltage.
• Adding more bulbs resistance goes up, current
goes down, and bulbs get dimmer
 Only one path for charges to flow.
• A break in a series circuit causes charges to stop
flowing; if one light in a series circuit goes out, the
other lights go out, too.
Parallel Circuit

Parallel circuit – a circuit that has more than
one path for the flow of electricity because
the parts are joined in branches or multiple
loops
Parallel Circuits:
Advantages and
Disadvantages
 Advantages:

 The voltage (potential difference) across
each part is the same.
• Each bulb will glow at full brightness
regardless of the number of bulbs.
 There are multiple paths for charges to
travel.
• If one bulb breaks, the other bulbs will
still work.
Disadvantages:
 The bulbs and batteries will die faster.
 Use more power
 The current is not the same in the
circuits
Household
Circuits

Combination of
parallel circuits
 too many devices
can cause wires
to overheat

Safety Features:
 fuse - metal
melts, breaking
the circuit
 circuit breaker bimetallic strip
bends when hot,
breaking the
Magnetism and Electromagnetism
S8P5. Students will recognize characteristics of
gravity, electricity, and magnetism as major kinds of
forces acting in nature.
c. Investigate and explain that electric currents and
magnets can exert force on each other.
Magnetism
 Magnetism
 The properties and interactions of
magnets
 Due to the arrangement of
electrons
 Closely related to electricity
Magnetic Force
 Magnetic
Force
 Force of attraction or
repulsion generated by moving
or spinning electric charges
 Increases as magnets move
closer together and decreases
as magnets move farther apart
Magnetic Poles

Magnetic Poles
 Regions on a magnet where the magnetic force
exerted by a magnet is the strongest
 Like poles repel.
 Opposite poles attract.
 A broken magnet creates new poles.
Magnetic Field
 Magnetic
Field
 Area around a magnet where
magnetic forces act
 Magnetic field lines show the
direction of the field (NS)

Molecular Expressions: Electricity and Magnetism - Interactive Java Tutorials: Magnetic Field
Lines
Earth’s Magnetic Field



Earth’s inner core is
made of a solid ball of
iron and nickel
surrounded by a liquid
layer of molten iron
and nickel.
The circulation of the
molten iron and nickel
in the Earth’s outer
core produces a
magnetic field.
Therefore, Earth acts
like a giant bar magnet.
Compass


A compass needle
is a small bar
magnet with a north
pole and a south
pole.
The needle aligns
with the magnetic
field lines of the
Earth’s Magnetic Poles

A compass’
needle points to
the north
geographic pole
due to the south
magnetic pole
being nearby.
 Magnetic poles
are NOT
aligned with
geographic
poles. They
Magnetic Domains

Magnetic Domains
 Groups of atoms with aligned magnetic poles
 Like tiny magnets of different sizes
domain
 In a magnetized object, the
domains are all aligned.
 In a non-magnetized object, the
domains are not aligned and
cancel each other out.
Magnetic Materials
 Few metals such as iron, cobalt,
and nickel are attracted to magnets
or can be made into permanent
magnets.
69
Types of Magnets
 Ferromagnets:
magnets
made of iron, nickel, cobalt, or
mixtures of these metals (ex.
magnetite)
 Electromagnets: magnets
formed when current passes
through a coil of wire
(solenoid) surrounding an iron
Permanent Magnets
 Permanent
Magnets
 Magnets that keep their
magnetism after they are
removed from a magnetic field
 Keep their magnetic properties
longer than temporary
magnets
 Some are made of alnico: an
alloy of aluminum, nickel,
Permanent Magnets
 Permanent
magnets can be
made:
 Place a magnetic material (iron,
cobalt, or nickel) in a strong
magnetic field.
 This causes the magnetic
domains in the material to line
up.
 This creates a strong magnetic
Temporary Magnets
 Temporary
Magnets
Magnets made from
materials that are easy to
magnetize
Tend to lose their
magnetism easily
 Ex. Soft iron items like
paperclips and nails
Magnetism in Nature
aurora
borealis
aurora
australis

Auroras
 They are formed when
charged particles from the
sun (known as solar wind)
hit oxygen and nitrogen
atoms in the air. The atoms
become excited and then
give off many colors of light.
 The charged particles can
crash into the atmosphere
at and near the magnetic
poles.
• North Pole
•
 Northern lights: aurora
borealis
South Pole
 Southern lights: aurora
Magnetism and Electricity


Moving charges,
like those in an
electric current,
produce
magnetic fields.
Around a currentcarrying wire the
magnetic field
lines form circles.
Magnetism and Electricity


As the current in
the wire
increases, the
strength of the
magnetic field
increases.
The direction of
the magnetic field
around the wire
reverses when
the direction of the
current in the wire
reverses.
Electromagnetism
 Electromagnetism
 The interaction between
electricity and magnetism
Solenoids
 Solenoid
 A single wire wrapped into a
cylindrical wire coil that produces
a magnetic field when electricity
passes through it.
 If wrapped around an iron core,
an electromagnet is formed.
Electromagnets
 Electromagnet
 A magnet formed when current
passes through a coil of wire
(solenoid) surrounding an iron
core
 The iron core becomes
magnetized only when current
flows through the wire.
Electromagnets
 The
strength of an electromagnet’s
magnetic field can be increased by:
 Adding more wraps of wire to the
solenoid
 Increasing the current passing
through the wire by increasing the
voltage.
 Increasing the size of the iron core
Properties of an
Electromagnet
 Has
a north and a south pole
 If placed in a magnetic field, it will
align itself along the magnetic field
lines
 Will attract magnetic materials and
be attracted or repelled by other
magnets
 Useful because the magnetic
properties can be controlled by
Electric Motors
 Electric Motors
 Devices that convert electrical energy into
mechanical energy Electric Motor
 An
electromagnet
rotates between
the poles of a
permanent
magnet.
Animation

Electromagnetic
Induction
 The process in which
an electric current is
produced in a wire by
changing a magnetic
field
 Michael Faraday
(1831), a British
scientist, discovered
this process.

An electric current can
be produced by moving
a magnet through a coil
of wire
Electromagn
etic
Induction
Electric Generators

Electric Generators
 Devices that use electromagnetic induction to
convert mechanical energy into electrical
energy
Electric Generator Animation
 As the crank is
GENERATOR
MOTOR
turned, the
rotating coil
crosses the
magnetic field
lines of the
magnet,
inducing a
current in the
wire.
Electric Generators

After the wire coil makes one-half of a revolution,
the ends of the coil are moving past the opposite
poles of the permanent magnet.
 This causes the current to change direction:
• Alternating Current (AC)
Electric
Generators

Examples:
 Power plants use
generators which have
many coils of wire
wrapped around huge
iron cores. The rotating
magnets are connected
to turbines which are
large wheels that rotate
when pushed by water,
wind, or steam.
• Nuclear power plants
use thermal energy
from a nuclear
reaction to boil water
into steam in order to
turn the turbines.
• Wind mills are
connected to
generators.
Electric Generators
 Example
 Hydroelectric
Dam
 The Potential
Energy (PE) of
lake water is
converted to
Kinetic Energy
(KE).
 Mechanical KE
turns the
generator shaft
which generates