Transcript File

Electricity
Brief summary of Chapter 16 - 18
Electrical Energy
Electrical energy comes from the movement of
electrons
Electrical energy is what comes out of a wall
socket
To produce electrical energy, a power source
such as a battery, generator, thundercloud, or
scuffing your shoes on a rug, moves electrons
from one atom to another
Uses of electrical energy
Millions of electrical signals race through a
human body each minute. Among other
things, they control nerves and muscles
Many species of fish use electrical energy
to stun or kill prey. Others, like sharks, can
track down prey by sensing the weak
electric signals generated by the muscles
of swimming fish
Uses (continued)
A flashlight and most alarm clocks are
powered by electrical energy. The power
source is a battery, which stores electricity
for future use
Warning: electric shock can cause muscle
spasms, shallow breath, weakness,
severe burns, and even death.
Charged!
There is only one type of electric energy. But it is
often split into two categories- static and
dynamic.
Greek scientist Thales (640-546 B.C.) first
recognized electrical effects. In an experiment,
he rubbed amber against silk. This caused
nearby lightweight objects, such as feathers, to
move toward the amber and cling to it.
Thales experiment
Normally, objects contain an equal number
of positive and negative electric charges,
which cancel each other out.
But by rubbing the amber, electrons are
transferred from atoms in the silk to atoms
in the amber, giving the amber a negative
charge.
Result
When the amber is held above a feather,
its negative charges repel the feather’s
negative charges, causing them to move
onto the ground the feather was touchingand the feather becomes positively
charged.
If the attraction is strong enough, the
positively charged feather will move
toward the negatively charged amber.
Static Electricity
What Thales did was show static electricity
in action.
The word electricity comes from the Greek
word for amber.
Dynamic Electricity
A steady flow of electrons between places
and things
It needs a conductor through which to flow,
such as copper
An energy source, such as a battery or
generator, starts the electrons moving
Static verses Dynamic
Static electricity is a buildup of electrons


It stays in one place until it jumps to another
object
Example ; the raising of hair after a balloon
has been rubbed against wool
Dynamic is the flow of electrons, called
current


Travels through a conductor like a wire
Example ; the electrical current that powers
appliances and machines, the current that
comes from a battery
Currents In Time
1600 – English scientist William Gilbert
launched the first serious study of
electricity and magnetism. He wanted to
know why both attracted things
1663 – German Otto Von Guericke finds
that spinning and rubbing a large sulfur
ball builds up static electricity
Currents In Time
1752 – Benjamin Franklin shows that
lightning is created by a buildup of static
electricity
1791 – Italian Luigi Galvani discovers that
a dead frog’s leg placed on a zinc tray
twitches when touched by an iron scalpel
that has been electrically charged.
Currents In Time
Alessandro Volta builds on the fact the
metals react with chemicals in the frogs
body to produce a battery. Volta makes a
battery using two metals and a chemical. A
volt is a measure used in electricity
Currents In Time
Late 1700s to early 1800s – Electricity
becomes a craze. Quack doctors shock
sick people to try to cure them. Many
believe electricity can revive the dead. In
the 1816 novel Frankenstein, a scientist
uses electricity to give life to a monster
made out of parts of dead bodies.
Currents In Time
1819 – Hans Christian Oersted of Denmark
notices that an electric current causes a
magnetized compass needle to act strangely.
Frenchman Andre Marie Ampere builds on his
work. Their work shows that electricity and
magnetism are different aspects of the same
force- electromagnetism. Ampere, or amp, is a
measure of electric current
Currents In Time
1821 – Michael Faraday of England
produces mechanical motion using a
magnet and an electric current. This is the
forerunner of the electric motor.
Later, he invents the dynamo, or
generator. It does the opposite- converts
mechanical motion into electric energy.
Currents In Time
1827 – German Georg Ohm shows how
electric circuits work. A circuit is any
system in which a current flows. Ohm
shows that the current depends on the
ability of the conductor to allow a charge to
move through it.
Currents In Time
Ohm continued – A fat wire is a better
conductor than a skinny wire made of the
same material. The thin wire is now called
a resistor and Ohms measure how good a
resistor ( or how poor a conductor)
something is.
Currents In Time
1837 – Samuel Morse invents the
telegraphs, allowing almost instant
communication. It’s the first electric
machine to change daily life.
1861- Scotsman James Clerk Maxwell
finds that light is a type of electromagnetic
energy. He predicts other types of EM
energy, such as radio waves. His work
leads to the idea that electromagnetism is
a basic force of the universe
Currents In Time
1879 – Thomas Edison creates the first
reliable, inexpensive light bulb
1883 – Nikola Tesla invents a motor that
ca produce an alternating current (AC)
rather than a direct current (DC). With
George Westinghouse’s backing, it
becomes the current used to power homes
and businesses.
Watt
The modern unit of power was named
after Scottish engineer James Watt who
developed the steam engine in the 1760s.
A watt measures the rate at which an
electrical current can do work.
Wattage x time shows how much work a
machine can produce, and thus the
amount of energy it uses to work
DC verses AC
In 1899, DC was the only way of delivering
electric power.
With a direct current the electric charges
(electrons) flow only one way in the circuit,
like runners going round and round a
track. DC is used for small machines like
flashlights.
DC verses AC
However, DC did not travel well over long
transmission lines. For that, we use
alternating current. With AC, the electric
charges vibrate very quickly back and
forth. It’s like an ocean tide rolling in and
out- only at the speed of light.
Electric motors
Produce mechanical power quickly and
quietly. In a simple electric motor, a loop of
wire (coil) is suspended in the magnetic
field between two magnets. The magnetic
field exerts a force on the electric current,
which flows through the coil. The force
causes the coil to rotate. As it rotates,
current continues to flow. This energy can
be used to do work, such as power
machines, from electric toothbrushes to
space satellites.
Electrical Energy Uses
Electrical energy can produce light,
generate heat, produce magnetic fields,
and change chemicals.
Electrons reach into all aspects of modern
life
Light
Many businesses use fluorescent or neon
lights, which pass an electric current
through a pressurized gas
Light
Most homes use the incandescent light
bulb. Its key part is a very thin, coiled wire,
called a filament, made of tungsten, a
tough metal.
As electrons move through the filament,
resistance causes it to heat up. The
filament reaches more than 4500° F, hot
enough to glow. A gas in the bulb keeps
the filament from burning up.
Appliances
Toasters, hair dryers, and many other
appliances work like light bulbs. But they
need to produce more heat than light.
Instead of a filament, they have a heating
element made of loops of wire made from
special mixtures of metals. Electrons move
through the wires, where electrical
resistance is high. That makes the heating
element warm up quickly.
Electrical signals
Calculators, DVD players, and other
electronics use electrical signals to create
their numbers, pictures, words, and
sounds.
The signals whiz through transistors that
are made of silicon. Silicon is a
semiconductor (a material that can be
changed to either conduct or resist an
electric current). Millions of transistors fit
on to one silicon chip.
Chemicals
Electrical energy unleashes big changes in
chemicals.
For example, passing a current through
salt water produces chlorine.
Chemicals
The silverware in most kitchens is not
made of pure silver. Instead, a silver
coating has been electroplated onto a
cheaper metal. In electroplating, a metal
item is hooked up to a negative charge
and dunked in a silver cyanide solution. A
positive electrode in the silver cyanide
causes silver atoms to cling evenly to the
metal.
Chemicals
Chemicals also produce electrical energy.
Batteries are the oldest artificial
electrochemical power plant.
They suck in electrons, thanks to the
chemical reaction between two elementsusually zinc and carbon – and an acid.
Chemicals
Fuel cells work like batteries.
They produce energy through the
chemical reaction of hydrogen, oxygen,
and an acid.
Batteries and fuel cells were both invented
in the 1800s. But fuel cells were largely
ignored until the 1960s, when they
became useful for U.S. moon missions.
The body electric
Every inch of a living body hums with
electrical activity. In fact, electrical energy
literally holds us together. It keeps solid
things solid. Our atoms would fly apart if
their electric charges did not attract one
another.
Human Body
The human body’s electrical signals are
weak. An electrocardiogram (ECG) is a
popular machine for reading them. It
shows the heart’s electrical impulses as a
series of wavy lines.
A bundle of nerves in the heart acts like an
electric power plant. If a heart stops
working properly, doctors may install a
pacemaker. It sends out electrical
impulses to keep the heart beating.
Animals
All living things give off small amounts of
electricity. But electric eels, the most powerful of
all electric fish, have special organs. They work
like high-powered generators and can stun or kill
prey with a strong shock.
One of the first Europeans to discover South
America’s electric eels made the mistake of
stepping on one. He wrote, “I was affected
during the rest of the day with violent pain in the
knees and in almost every joint.”
Medicine
Other electric fish deliver a weaker shock.
Ancient Romans believed that putting one
on someone’s head could jolt a headache
away. They may have been on to
something.
Scientists have found that small, controlled
electrical currents can relieve pain. They
have also found that electrical currents
can speed up the healing of wounds and
regenerate damaged nerves.
Medicine
In 1924, German psychiatrist Hans Berger
pasted two small pieces of silver foil to his
15-year-old son’s scalp, attached wires to
them, and connected the wires to a
galvanometer, which measures electric
current.
This was the forerunner of the
electroencephalogram (EEG).
EEG
It showed electric signals called brain
waves. It’s still not clear where in the brain
the signals come from, but they change
form one activity to another, and at times,
even during a single activity.
For example, a normal sleep pattern
includes periods of REM (rapid eye
movement), when we do most of our
dreaming. An EEG during REM and nonREM varies.
Defense
The body’s electrical nature can be used
against it. About one-quarter of U.S. police
agencies now use Tasers, or stun guns, to
control unruly suspects.
Tasers throw two darts as far as 221 feet.
The darts deliver a painful five-second
shock of up to 50,000 volts, causing
muscles to go rigid. The suspect quickly
recovers.
The power of change
The world has seen two revolutions on power.
Steam engines kicked off the first one in the late
1700s. They provided steady mechanical
energy.
Electricity brought about the second revolution in
the late 1800s. It created a wired world with
countless gadgets for our convenience.
A new revolution is in the making to find ways to
use electricity with out burning fossil fuels.
Green Energy
Some states are moving toward distributed
generation of power. That means that
homeowners produce their own electrical
energy using fuel cells, solar panels, or
some other green energy.
Saudi Arabia has solar powered
telephones beside the highways
Cars
Car engines need oil to run, but oil is
running out. An alternative may be electric
cars.
Car manufacturers already produce
hybrids. They are fueled partly by an
electric battery. Electric cars that use lowpolluting fuel cells have also been
introduced. So far, these vehicles make up
only a fraction of the world’s hundreds of
millions of cars.
Cell phone
Powering up a cell phone may be as easy
as walking to school. Scientists are
working to turn human movement into
electrical energy using piezoelectric
crystals (crystals that are squeezed or
made to vibrate).
Putting crystals in a shoe’s heel could
produce enough energy to fuel a small
appliance.
Renewable energy
Wind, sun (solar), and other renewable
power resources are good energy choices.
But they are more costly than traditional
sources. Fortunately, that is changing.
Some experts say that by the middle of
this century, wind could supply 10 to 20
percent of the world’s electrical energy
needs.
Power system
Keeping the present power system could be a
challenge. The North American power grid is
becoming old. Many power companies have
failed to update or take care of equipment.
August 2003, minor troubles at one Ohio power
company, coupled with human error, triggered a
massive blackout. More than 50 million people in
seven northeastern states and Canada lost
power.
Current power division
2% from solar, wind, others
3% from oil
6% from hydro power (dams)
17% from natural gas
21% from nuclear
51% from coal