Transcript Electrical Energy

Table of Contents
Types of Energy
•Mechanical
•Thermal
•Chemical
•Nuclear
•Electrical
•Radiant
4
Mechanical Energy Review
• ME = PE + KE
• KE = ½ m v2
greatest at
position 2
• GPE = mgh
greatest at
position 1 and 5
6.1
Thermal Energy
The sum of the kinetic and potential energy of
all the particles in an object is the thermal
energy of the object.
Temperature and Heat
6.1
Matter in Motion
• The faster they move, the more kinetic
energy they have.
• This figure shows that particles move faster
in hot objects than in cooler objects.
Transferring Thermal Energy
6.2
Transfer Thermal Energy
• Thermal energy is transferred when one
end of a metal spoon is heated by a Bunsen
burner.
• The kinetic energy of
the particles near the
flame increases.
Transferring Thermal Energy
6.2
Transfer Thermal Energy
• Kinetic energy is transferred when these
particles collide with neighboring particles.
• As these collisions
continue, thermal
energy is transferred
from one end of the
spoon to the other end
of the spoon.
Transferring Thermal Energy
6.2
Radiant Energy and Matter
• Different materials on
Earth absorb radiation in
different amounts resulting
in uneven heating.
• Sea breezes and Land
breezes are examples of
this.
• Natural convection
currents are created.
Using Heat
6.3
Internal Combustion Engines
• A car engine is an internal combustion engine
• Each cylinder contains a piston that moves
up and down (a stroke).
• The heated material in the cylinders
expands forcing the piston down.
• As exhaust gases are released, the piston
comes up.
• As the crankshaft moves with the piston, it
turns vital parts of the car.
Using Heat
6.3
Internal Combustion Engines
Chemical Energy
• Chemical energy comes from energy
release when chemical bonds are broken
or formed.
• When we eat, we break the bonds in our
food to release energy to be used by our
body.
• Same goes for chemical fuel used for
other reasons.
9.1
Chemical Energy Sources
• Compared to other fuels such as wood, the
chemical energy that is stored in fossil fuels
is more concentrated.
• For example,
burning 1 kg of coal
releases two to three
times as much
energy as burning 1
kg of wood.
Fossil Fuels
9.1
Petroleum
• Petroleum is a highly flammable liquid formed
by decayed ancient organisms, such as
microscopic plankton and algae.
• It is one of the fossil fuels.
• The key ingredient to fossil fuel
is a carbon hydrogen bond
called a hydrocarbon.
Carbon is found in all living and once living things.
9.2
Nuclear Energy
• Nuclear Energy is a type of chemical energy
• A nuclear power plant generates electricity
using the energy released in nuclear fission.
• The sun generates energy
transferred as light
by nuclear fusion.
Nuclear Fission
9.2 When a neutron strikes the nucleus of a U-235
atom, the nucleus splits apart into two
smaller nuclei.
In the process
-two or three neutrons
are emitted,
-smaller nuclei are
called fission products
of barium and krypton
are created,
-and energy is released
.
9.2
Nuclear Fusion
Thermonuclear fusion is the joining together of
small nuclei at high temperatures.
•2 hydrogen atoms fuse to form a helium atom
of less mass
•The mass lost turns into energy by E=mc2
7.1
Electrical Energy
• Atoms contain particles called protons,
neutrons, and electrons.
• Protons are
positively charged
• Electrons have a
negative charge,
• Neutrons have no
electric charge.
Electric Charge
7.1
Static Electricity
• When you walk on the
carpet, electrons are
transferred from the carpet
to the soles of your shoes.
• Your shoe soles become negatively charged.
• The carpet lost electrons and is positively
charge.
• The accumulation of excess electric charge
on an object is called static electricity.
Static Charge
7.1
Lightning
• Lightning is a large static discharge.
• A static discharge is a transfer of charge
between two objects
• A thundercloud is a mighty generator of static
electricity. As air masses move and swirl in
the cloud, areas of positive and negative
charge build up.
Static Charge
7.1
Lightning
• Eventually, enough charge builds up to cause
a static discharge between the cloud and the
ground.
• As the electric charges
move through the air,
they collide with atoms
and molecules. These
collisions cause the
atoms and molecules
in air to emit light.
Electric Current
7.2
Current and Voltage Difference
• The net movement of electric charges in a
single direction is an electric current.
• When an electric current flows in the wire,
electrons drift in the direction that the current
flows.
• Electric current is measured in amperes
(Amps).
Electric Current
7.2
Voltage Difference
• Electric charge flows from higher voltage to
lower voltage.
• A voltage difference
is related to the force
that causes electric
charges to flow.
Voltage difference is
measured in volts.
Electric Charge
7.1
Conservation of Charge
• Law of conservation of charge, charge can be
transferred, but it cannot be created or
destroyed.
• Whenever an object becomes charged, electric
charges have moved from one place to
another.
Electric Charge
7.1
Conductors
• A material in which electrons are able to
move easily is a conductor.
• The best electrical conductors are metals.
• The atoms in metals have electrons that are
able to move easily through the material.
Electric Charge
7.1
Insulators
• A material in which electrons are not able
to move easily is an insulator.
• Electrons are held tightly to atoms in
insulators.
• Most plastics are insulators.
• The plastic coating
around electric wires
prevents a dangerous
electric shock when
you touch the wire.
Electric Current
7.2
Electric Circuits
• A closed path that electric current follows is a
circuit.
• If the circuit is
broken by removing
the battery, or the
light bulb, or one of
the wires, current
will not flow.
Electric Current
7.2
Resisting the Flow of Current
• Resistance is the tendency for a material to
oppose the flow of electrons, changing
electrical energy into thermal energy and
light.
• Resistance is measured in ohms ().
• Depends on temperature, length, and
diameter: hotter, longer, thinner increases
resistance
Electric Current
7.2
Ohm's Law
• The voltage difference, resistance, and
current in a circuit are related.
• According to Ohm's law, the current in a
circuit equals the voltage difference divided
by the resistance.
• Ohm's law provides a way to measure the
resistance of objects and materials. First the
equation above is written as: I = V/R
Electrical Energy
7.3
Series Circuits
• One kind of circuit is called a series circuit.
• In a series circuit,
the current has only
one loop to flow
through.
• Series circuits are
used in flashlights
and some holiday
lights.
Electrical Energy
7.3
Parallel Circuits
• Houses are wired with parallel circuits.
• Parallel circuits contain two or more
branches for current to move through.
• The current can
flow through
both or either of
the branches.
Electrical Energy
7.3
Household Circuits
• The main switch and circuit breaker or fuse
box serve as an electrical headquarters for your
home.
• Parallel
circuits branch
out from the
box to wall
sockets, major
appliances,
and lights.
Electrical Energy
7.3
Household Circuits
• To protect against overheating of the wires,
all household circuits contain either a fuse or
a circuit breaker.
• The rate at
which electrical
energy is
converted to
another form of
energy is the
electric power.
Magnetism
8.1
Magnetic Domains
• Magnetic material contains domains of
enormous number of atoms that align their
charges.
• Domains are also
aligned creating a
magnetic field with
polar ends.
Magnetism
8.1
Magnetic Field
• A magnetic field exerts a
force on other magnets
and objects made of
magnetic materials.
• The magnetic field is
strongest close to the
magnet and weaker far
away.
• The field also has
direction.
Magnetism
8.1
Magnetic Poles
• Magnetic poles are
where the magnetic
force exerted by the
magnet is strongest.
• Like poles (ie.2 north poles or 2 south poles)
repel each other.
• Opposite poles (ie. north poles and south
poles) attract each other.
Magnetism
8.1
Earth’s Magnetic Field
The earth is a large
magnet due to a
solid inner core of
iron and nickel
surrounded by a
spinning layer of
liquid iron and
nickel.
Magnetism
8.1
Earth’s Magnetic Field
• A compass can help
determine direction
because the north
pole of the compass
needle points to the
northern geographic
pole which is
actually a south
magnet pole.
Electricity and Magnetism
8.2
Moving Charges and Magnetic
Fields
• It is now known that moving charges, like
those in an electric current, produce magnetic
fields.
• Around a
currentcarrying wire
the magnetic
field lines
form circles.
Electricity and Magnetism
8.2
Electromagnets
• An electromagnet is a temporary magnet
made by wrapping a wire coil carrying a
current around an iron core.
• The magnetic field inside the loop is
stronger than the field around a straight
wire.
• A single wire
wrapped into a
cylindrical wire
coil is called a
solenoid.
Electricity and Magnetism
8.2
Electric Motors
• An electric motor is a device that changes
electrical energy into mechanical energy.
• Step 1. When a
current flows in the
coil, the magnetic
forces between the
permanent magnet
and the coil cause
the coil to rotate.
Electricity and Magnetism
8.2
Making the Motor Spin
• Step 2. In this position, the brushes are not in
contact with the commutator and no current
flows in the coil.
• The inertia of
the coil keeps it
rotating.
Electricity and Magnetism
8.2
Making the Motor Spin
• Step 3. The commutator reverses the
direction of the current in the coil.
• This flips the
north and south
poles of the
magnetic field
around the coil.
Electricity and Magnetism
8.2
Making the Motor Spin
• Step 4. The coil rotates until its poles are
opposite the poles of the permanent magnet.
• The
commutator
reverses the
current, and
the coil keeps
rotating.
Producing Electric Current
8.3
Generators
• A generator uses electromagnetic induction
to transform mechanical energy into
electrical energy.
• In this type of generator,
a current is produced in
the coil as the coil rotates
between the poles of a
permanent magnet.
Producing Electric Current
8.3
Generating Electricity for Homes
The rotating magnets are connected to a turbine, a
large wheel that rotates when pushed by water,
wind, or steam.
Producing Electric Current
8.3
Direct and Alternating Currents
• A battery produces a direct current.
• Direct current (DC) flows only in one
direction through a wire.
• Power companies produce alternating
current (AC) reverses the direction of the
current in a regular pattern.
Producing Electric Current
8.3
Transmitting Electrical Energy
• When the electric energy is transmitted along
power lines, some of the electrical energy is
converted into heat due to the electrical
resistance of the wires.
• The electrical
resistance and heat
production increases
as the wires get
longer.
Producing Electric Current
8.3
Transmitting Electrical Energy
• One way to reduce the heat produced in a
power line is to transmit the electrical
energy at high voltages, typically around
150,000 V.
• Electrical energy at such high voltage cannot
enter your home safely, nor can it be used in
home appliances.
• A transformer is used to decrease the
voltage.
Producing Electric Current
8.3
Transformers
• A transformer is a device that increases or
decreases the voltage of an alternating
current.
• A transformer is
made of a primary
coil and a
secondary coil.
• These wire coils are
wrapped around the
same iron core.
Producing Electric Current
8.3
Transformers
A transformer that
increases the voltage so
that the output voltage
is greater than the input
voltage.
• A transformer that
decreases the
voltage so that the
output voltage is
less than the input
voltage.
Producing Electric Current
8.3
Transmitting Alternating Current
• This figure shows how step-up and step-down
transformers are used in transmitting electrical
energy from power plants to your home.
The Nature of Waves
10.1
• A wave is a repeating disturbance or
movement that transfers energy through
matter or space.
• The waves don’t carry matter along with
them. Only the energy carried by the
waves moves forward.
• A wave will travel only as long as it has
energy to carry.
The Nature of Waves
10.1
Mechanical Waves
• Mechanical waves are waves that travel
through matter.
• The matter the waves travel through is
called a medium.
• The medium can be a solid, a liquid, a
gas, or a combination of these.
Types of Mechanical of Waves
10.1
• A compressional
wave moves back
and forth.
• A transverse wave
moves up and down.
Examples of Mechanical Waves
10.1
Water Waves a
mechanical wave of a
combination of
transverse and
compression action.
Seismic Waves are
also a combination of
both actions that go
through the Earth’s
crust
Wave Properties
10.2
The Parts of a Wave
• A transverse wave has alternating high
points, called crests, and low points, called
troughs.
Wave Properties
10.2
Wavelength
• A wavelength is the distance between one
point on a wave and the nearest point just
like it.
• For transverse
waves the
wavelength is the
distance from
crest to crest or
trough to trough.
Wave Properties
10.2
Frequency and Period
• The frequency of a wave is the number
of wavelengths that pass a fixed point
each second.
• You can find the frequency of a transverse
wave by counting the number of crests or
troughs that pass by a point each second.
• Frequency is expressed in hertz (Hz).
Wave Properties
10.2
Calculating Wave Speed
• You can calculate the speed of a wave
represented by v by multiplying its frequency
times its wavelength.
Wave Properties
10.2
Amplitude of Transverse Waves
• The amplitude of any transverse wave is
the distance from the crest or trough of the
wave to the rest position of the medium.
The Behavior of Waves
10.3
The Law of Reflection
• The beam striking
the mirror is called
the incident beam.
• The beam that
bounces off the
mirror is called
the reflected
beam.
The Behavior of Waves
10.3
Refraction
• Refraction is the
bending of a wave
caused by a change
in its speed as it
moves from one
medium to another.
The Behavior of Waves
10.3
Diffraction
• Waves also can be diffracted when they
pass through a narrow opening.
• After they pass
through the
opening, the waves
spread out and
bend.
The Behavior of Waves
10.3
Interference
• When two or more
waves overlap and
combine to form a
new wave, the
process is called
interference.
Interference occurs
while two waves
are overlapping.
The Behavior of Waves
10.3
Constructive Interference
• In constructive interference, the waves
add together.
• The amplitude of
the new wave
that forms is
equal to the sum
of the amplitudes
of the original
waves.
The Behavior of Waves
10.3
Destructive Interference
• In destructive interference, the waves
subtract from each other as they overlap.
• This happens
when the crests
of one
transverse wave
meet the troughs
of another
transverse wave.
What are electromagnetic waves?
12.1
Electromagnetic Waves
• Electromagnetic waves are made by
vibrating electric charges and can travel
through space where matter is not present.
• Instead of transferring energy from particle
to particle, electromagnetic waves travel by
transferring energy between vibrating
electric and magnetic fields.
What are electromagnetic waves?
12.1
Wave Speed
• All electromagnetic waves travel at 300,000
km/s in the vacuum of space.
• The speed of electromagnetic waves in space
is usually called the “speed of light.”
• As the frequency increases, the wavelength
becomes smaller.
What are electromagnetic waves?
12.1
Waves and Particles
• Energy carried by a wave depends on its
amplitude and not its frequency.
• Albert Einstein stated electromagnetic waves
can behave as a particle, called a photon,
whose energy depends on the frequency of
the waves.
The Electromagnetic Spectrum
12.2
A Range of Frequencies
• Electromagnetic waves can have a wide
variety of frequencies.
• The entire range of electromagnetic wave
frequencies is known as the electromagnetic
spectrum.
The Electromagnetic Spectrum
12.2
Visible Light
• Visible light is the range of electromagnetic
waves that you can detect with your eyes.
• Visible light has wavelengths around 750
billionths to 400 billionths of a meter.
The Behavior of Light
13.1
Radiant Energy and Light
•Light is the result of radiant energy traveling
in electromagnetic waves that hit materials
and excite the material’s electrons.
•Those electrons move farther away from the
nucleus
• When it returns the electron gives off
photons of electromagnetic waves.
The Behavior of Light
13.1
The Law of Reflection
• Because light behaves as a wave, it obeys
the law of reflection.
• According to the
law of reflection,
light is reflected
so that the angle
of incidence
always equals the
angle of
reflection.
Light and Color
13.2
Colors
• An object’s color depends on the wavelengths
of light it reflects.
• You know that white light is a blend of all
colors of visible light.
• This image shows
white light striking
a green leaf. Only
the green light is
reflected to your
eyes.
The Behavior of Light
13.1
Refraction and Rainbows
• Refraction is caused by a change in the speed of
a wave when it passes from one material to
another.
• The refraction of the different wavelengths
can cause white light from the Sun to
separate into the individual colors of visible
light.
• Like prisms, rain
droplets also refract
light.
Light and Color
13.2
Light and the Eye
• In a healthy eye, light enters and is focused on
the retina, an area on the inside of your eyeball.
• The retina is made up of two types of cells that
absorb light.
• These cells absorb light
energy, chemical
reactions convert light
energy into nerve
impulses that are
transmitted to the brain.
Light and Color
13.2
Light and the Eye
• One type of cell in the retina, called a cone,
allows you to distinguish colors and detailed
shapes of objects and are most effective in
daytime vision.
• The second type of cell, called a rod, is sensitive
to dim light and is useful for night vision.
• Red, green, and blue are the primary colors of
light. When mixed together in equal amounts
they produce white light.
Light and Color
13.2
Mixing Colors
• A pigment is a colored material that is used to
change the color of other substances.
• The color of a pigment results from the
different wavelengths of light that the pigment
reflects.
• A primary pigment’s color depends on the
color of light it reflects.
• If all the primary light colors are reflected in
equal amounts, the object appears white.
Mirrors
14.1
Mirrors
• The image formed when an object is placed
by a mirror changes depending on its position
in relation to the mirror’s focal point.
• If the surface of a mirror
is curved inward, it is
called a concave mirror.
•The mirrors are
often used to
magnify objects.
Mirrors
14.1
Convex Mirrors
• A mirror that curves outward like the back of
a spoon is called a convex mirror.
• Objects tend to
appear smaller
and farther
away such as in
rear view and
side mirrors of
cars.
Lenses
14.2
What is a lens?
• A lens is a transparent material with at least
one curved surface that causes light rays to
bend, or refract, as they pass through.
• The image that a lens forms depends on the
shape of the lens.
• The type of image a lens forms depends on
where the object is relative to the focal point.
• Like curved mirrors, a lens can be convex or
concave.
Lenses
14.2
Convex Lenses
• A convex lens is thicker in the middle than at
the edges.
• When the candle is
more than two focal
lengths away from
the lens, its image is
real, reduced, and
upside down.
Lenses
14.2
Concave Lenses
• A concave lens is thinner in the middle and
thicker at the edges.
• The image is
always virtual,
upright, and
smaller than
the actual
object is.
Lenses
14.2
Focusing on Near and Far
• As an object gets farther from your eye, the
focal length of the lens has to increase.
• The muscles
around the
lens stretch
it so it has a
less convex
shape.
Lenses
14.2
Focusing on Near and Far
• But when you focus on a nearby object, these
muscles make the lens more curved, causing
the focal length to decrease.
Lenses
14.2
Vision Problems—Farsightedness
• If you can see distant objects clearly but can’t
bring nearby objects into focus, then you are
farsighted.
Lenses
14.2
Farsightedness
• To correct the problem, convex lenses cause
incoming light rays to converge before they
enter the eye.
Lenses
14.2
Astigmatism
• Another vision problem, called astigmatism
occurs when the surface of the cornea is
curved unevenly.
• When people have astigmatism, their corneas
are more oval than round in shape.
• Astigmatism causes blurry vision at all
distances.
Lenses
14.2
Nearsightedness
• If you have nearsighted friends, you know
that they can see clearly only when objects
are nearby.
• When a nearsighted
person looks at
distant objects, the
light rays from the
objects are focused
in front of the
retina.
Lenses
14.2
Nearsightedness
• A concave lens in front of a nearsighted eye
will diverge the light rays so they are focused
on the retina.