14 EET 20 30 What is Electricity and what is a Watt
Electricity is the flow of electrical power or charge. It is a secondary energy source which means
that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear
power and other natural sources, which are called primary sources. The energy sources we use
to make electricity can be renewable or non-renewable, but electricity itself is neither renewable
nor non-renewable.
Electricity is a basic part of nature and it is one of our most widely used forms of energy. Many
cities and towns were built alongside waterfalls (a primary source of mechanical energy) that
turned water wheels to perform work. Before electricity generation began over 100 years ago,
houses were lit with kerosene lamps, food was cooled in iceboxes, and rooms were warmed by
wood-burning or coal-burning stoves. Beginning with Benjamin Franklin's experiment with a kite
one stormy night in Philadelphia, the principles of electricity gradually became understood.
Thomas Edison helped change everyone's life -- he perfected Sir Joseph Wilson Swan invention
-- the electric light bulb. Prior to 1879, direct current (DC) electricity had been used in arc lights
for outdoor lighting. In the late-1800s, Nikola Tesla pioneered the generation, transmission, and
use of alternating current (AC) electricity, which can be transmitted over much greater
distances than direct current. Tesla's inventions used electricity to bring indoor lighting to our
homes and to power industrial machines.
Despite its great importance in our daily lives, most of us rarely stop to think what life would be
like without electricity. Yet like air and water, we tend to take electricity for granted. Every day,
we use electricity to do many jobs for us -- from lighting and heating/cooling our homes, to
powering our televisions and computers. Electricity is a controllable and convenient form of
energy used in the applications of heat, light and power.
A battery produces electricity using two different metals in a chemical solution. A chemical
reaction between the metals and the
chemicals frees more electrons in one metal
than in the other. One end of the battery is
attached to one of the metals; the other end is
attached to the other metal. The end that
frees more electrons develops a positive
charge and the other end develops a negative
charge. If a wire is attached from one end of
the battery to the other, electrons flow
through the wire to balance the electrical
charge. A load is a device that does work or
performs a job. If a load––such as a light
bulb––is placed along the wire, the electricity
can do work as it flows through the wire. In
the picture above, electrons flow from the
negative end of the battery through the wire
to the light bulb. Electricity flows through the wire in the light bulb and back to the battery.
A generator is a device that converts mechanical energy into electrical energy. The process is
based on the relationship between magnetism and electricity. In 1831, Faraday discovered that
when a magnet is moved inside a coil of wire, electrical current flows in the wire.
A typical generator at a power plant uses an electromagnet—a magnet produced by electricity—
not a traditional magnet. The generator has a series of insulated coils of wire that form a
stationary cylinder. This cylinder surrounds a rotary electromagnetic shaft. When the
electromagnetic shaft rotates, it induces a small electric current in each section of the wire coil.
Each section of the wire becomes a small, separate electric conductor. The small currents of
individual sections are added together to form one large current. This current is the electric
power that is transmitted from the power company to the consumer.
An electric utility power station uses either a turbine, engine, water wheel, or other similar
machine to drive an electric generator or a device that converts mechanical or chemical energy
to generate electricity. Steam turbines, internal-combustion engines, gas combustion turbines,
water turbines, and wind turbines are the most common methods to generate electricity. Most
power plants are about 35 percent efficient. That means that for every 100 units of energy that
go into a plant, only 35 units are converted to usable electrical energy.
Most of the electricity in the United States is produced in steam turbines. A turbine converts the
kinetic energy of a moving fluid
(liquid or gas) to mechanical
energy. Steam turbines have a
series of blades mounted on a
shaft against which steam is
forced, thus rotating the shaft
connected to the generator. In a
fossil-fueled steam turbine, the
fuel is burned in a furnace to heat
water in a boiler to produce
steam. Coal, petroleum (oil), and
natural gas are burned in large
furnaces to heat water to make
steam that in turn pushes on the
blades of a turbine.
Did you know that most electricity generated in the United State comes from burning coal? In
2006, nearly half (49%) of the country's 4.1 trillion kilowatt-hours of electricity used coal as its
source of energy.
https://www.youtube.com/watch?v=rEJKiUYjW1E
Natural gas, in addition to being burned to heat water for
steam, can also be burned to produce hot combustion
gases that pass directly through a turbine, spinning the
blades of the turbine to generate electricity. Gas turbines
are commonly used when electricity utility usage is in high
demand. In 2006, 20% of the nation's electricity was fueled by natural gas.
Petroleum can also be used to make steam to turn a turbine. Residual fuel oil, a product refined
from crude oil, is often the petroleum product used in electric plants that use petroleum to
make steam. Petroleum was used to generate about two percent (2%) of all electricity
generated in U.S. electricity plants in 2006.
https://www.youtube.com/watch?v=Em1crnEt45Q
Nuclear power is a method in which steam is produced by heating water through a process
called nuclear fission. In a nuclear power plant, a reactor contains a core of nuclear fuel,
primarily enriched uranium. When atoms of uranium fuel are hit by neutrons they fission (split),
releasing heat and more neutrons. Under controlled conditions, these other neutrons can strike
more uranium atoms, splitting more atoms, and so on. Thereby, continuous fission can take
place, forming a chain reaction releasing heat. The heat is used to turn water into steam,
which, in turn, spins a turbine that generates electricity. Nuclear power was used to generate
19% of all the country's electricity in 2006.
https://www.youtube.com/watch?v=_UwexvaCMWA
Hydropower, the source for almost 7% of U.S. electricity generation in 2006, is a process in
which flowing water is used to
spin a turbine connected to a
generator. There are two basic
types of hydroelectric systems
that produce electricity. In the
first system, flowing water
accumulates in reservoirs
created by the use of dams.
The water falls through a pipe
called a penstock and applies
pressure against the turbine
blades to drive the generator
to produce electricity. In the
second system, called run-ofriver, the force of the river
current (rather than falling
water) applies pressure to the
turbine blades to produce electricity.
https://www.youtube.com/watch?v=rnPEtwQtmGQ
Geothermal power
comes from heat energy
buried beneath the
surface of the earth. In
some areas of the
country, enough heat
rises close to the surface
of the earth to heat
underground water into
steam, which can be
tapped for use at steamturbine plants. This
energy source generated
less than 1% of the
electricity in the country
in 2006.
https://www.youtube.com/watch?v=kjpp2MQffnw
Solar power is derived from
the energy of the sun.
However, the sun's energy is
not available full-time and it
is widely scattered. The
processes used to produce
electricity using the sun's
energy have historically
been more expensive than
using conventional fossil
fuels. Photovoltaic
conversion generates electric
power directly from the light of the sun in a photovoltaic (solar) cell. Solar-thermal electric
generators use the radiant energy from the sun to produce steam to drive turbines. In 2006,
less than 1% of the nation's electricity was based on solar power.
https://www.youtube.com/watch?v=tdivW7inP0k
Wind power is derived from the
conversion of the energy contained in
wind into electricity. Wind power, less
than 1% of the nation's electricity in
2006, is a rapidly growing source of
electricity. A wind turbine is similar to a
typical wind mill.
https://www.youtube.com/watch?v=0Kx
3qj_oRCc
Biomass includes wood, municipal solid
waste (garbage), and agricultural
waste, such as corn cobs and wheat
straw. These are some other energy
sources for producing electricity. These
sources replace fossil fuels in the
boiler. The combustion of wood and
waste creates steam that is typically
used in conventional steam-electric
plants. Biomass accounts for about 1%
of the electricity generated in the
United States.
https://www.youtube.com/watch?v=jbQ1hw7XQ0M
Electricity is measured in units of power called watts. It was named to honor James Watt, the
inventor of the steam engine. One watt is a very small amount of power. It would require
nearly 750 watts to equal one horsepower. A kilowatt represents 1,000 watts. A kilowatt-hour
(kWh) is equal to the energy of 1,000 watts working for one hour. The amount of electricity a
power plant generates or a customer uses over a period of time is measured in kilowatt-hours
(kWh). Kilowatt-hours are determined by multiplying the number of kW's required by the
number of hours of use. For example, if you use a 40-watt light bulb 5 hours a day, you have
used 200 watt-hours, or 0.2 kilowatt-hours, of electrical energy.
Electrical power is measured in watts. In an electrical system power (P) is equal to the voltage
multiplied by the current.
P = VI
ELECTRICAL EFFICIENCY
Electrical systems are more efficient when a higher voltage is used to reduce current. In an
electrical system, increasing either the current or the voltage will result in higher power. Let's
say you have a system with a 6-volt light bulb hooked up to a 6-volt battery. The power output
of the light bulb is 100 watts. Using the equation above, we can calculate how much current in
amps would be required to get 100 watts out of this 6-volt bulb.
You know that P = 100 W, and V = 6 V. So you can rearrange the equation to solve for I and
substitute in the numbers.
l = P/V = 100W/6V = 16.66amps
What would happen if you use a 12-volt battery and a 12-volt light bulb to get 100 watts of
power?
100 W/12 V = 8.33 amps. So this system produces the same power, but with half the current.
There is an advantage that comes from using less current to make the same amount of power.
The resistance in electrical wires consumes power, and the power consumed increases as the
current going through the wires increases. You can see how this happens by doing a little
rearranging of the two equations. What you need is an equation for power in terms of
resistance and current.
Let's rearrange the first equation:
l = V/R can be restated as V = I x R Now you can substitute the equation for V into the other
equation:
P = I V substituting for V we get P = IR I, or P = I2R
What this equation tells you is that the power consumed by the wires increases if the resistance
of the wires increases (for instance, if the wires get smaller or are made of a less conductive
material). But it increases dramatically if the current going through the wires increases. So
using a higher voltage to reduce the current can make electrical systems more efficient. The
efficiency of electric motors also improves at higher voltages. This improvement in efficiency is
what is driving the automobile industry to adopt a higher voltage standard.
Carmakers are moving toward a 42-volt electrical system from the current 12- volt electrical
systems. The electrical demand on cars has been steadily increasing since the first cars were
made.
The first cars didn't even have electrical headlights; they used oil lanterns. Today cars have
thousands of electrical circuits, and future cars will demand even more power. The change to
42 volts will help cars meet the greater electrical demand placed on them without having to
increase the size of wires and generators to handle the greater current.
To help you remember, you can call it the West Virginia Law:
W = VA
That is, Watts = Volts * Amps.
Watts are a measure of power, which is work being done at a particular rate. That's why the
power company charges you for kilowatt-hours: the rate of work per hour, times the number of
hours. "Power" can be a little bit of work done quickly, like one small light bulb glowing very
brightly, or a lot of work done slowly, like gradually charging up a car battery.
"Work" happens when something gives off light or heat, or when it moves. A light bulb or hair
dryer is measured in watts: the higher the wattage, the faster it's doing its work, putting out
more light or heat.
A Watt is defined as 1 joule/second. A "joule" is a unit of energy. In the case of electricity, it
means you've pushed a certain number of electrons (measured in "coulombs", which I'll get
back to in a second) across a certain voltage. The more electrons you push, and the harder you
push them, the more light you get out of your light bulb.
"How hard you push" is measured in Volts. Voltage is like gravity, for electrical force. It's
measured as the difference between two places. When you push a car off a cliff, the total
amount of energy it gets is the difference between the cliff and the ground. With electricity, you
have two wires from the power company, and the voltage is the electrical force between them.
Connect them together, and current will flow with a particular force.
That "current" is how many electrons are moving past a point at a particular point in time. "How
many electrons" is that coulomb again? The current is measured in amperes, which is a
coulomb per second.
This is a lot of things to take in all at once, and it helps to think of it by analogy with water:
• A coulomb (number of electrons) is like a gallon of water • An ampere (current) is like a
gallon of water moving by in one second, just like water current • A volt (voltage) is like a cliff
that a waterfall is going over
• A watt (that is, volts * amps, voltage * current) is how fast work can be done by water going
over the waterfall: how many gallons per second, and how hard they hit the bottom.
• A watt-second (or kilowatt-hour; same thing on a different scale) is the amount of work done
by that water hitting the ground in 1 second.
People often used amps and watts interchangeably because for houses, the voltage is always
the same: 110V. So if I tell you that this microwave draws 15 amps, you know how much
power it uses:
15 amps * 110 V = -1,500 W. Run your 1,500W microwave for an hour, and they'll charge you
for 1.5 kilowatt-hours.
Looking at it in terms of electrons is just a bit more complicated, because there are two kinds of
electricity. (Well, two main kinds) The simple kind is "Direct current", which really is just
electrons flowing through a wire. That's the kind used inside electronic devices.
But that's not what comes into your house. What you get in your house is Alternating Current
(AC). You don't actually get a flow of electrons. Instead, you get electrons pushed back and
forth, a lot like the wave of the ocean. Thus, the actual power, voltage, and current actually
vary cyclically, 60 times a second.
It turns out, though, that averaged over time, they're still doing about the same amount of
work. Both the up-flows and down-flows of the wave are doing work. That's easiest to see in
the case of a light bulb. The filament gets hot when electrons flow through it, but it doesn't
matter which way the electrons are flowing. Strictly speaking, there's an instant (two instants,
really) in each cycle where there are no electrons flowing, but the bulb stays hot through that
instant.
The bulb fluctuates very, very, very faintly because of it, but too faintly for your eyes to see and
far too fast.
The wall wart that you use to connect electronic objects to the socket both converts electricity
from high voltage to a reasonable amount, and sometimes converts it from AC to DC. It turns
out that's not hard. You just send the current through one wire when it's going up, and another
wire that reverses it when it's going down, and you get a continuous stream with a constant
voltage.
Remember: the voltage is how much force the electrons move with. A small device like a
calculator can't handle a lot of force, even if it's a small amount of electricity. It would be like
trying to water a flower pot with your finger over the hose: the water squirts out in a very
sharp stream, knocking over the plant. The same amount of water in the same time is more
controllable when it comes out with less force.