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Efficiency
Incandescent light bulbs were invented over 150 years
ago
Today, billions of light bulbs (lamps) illuminate vast areas
of Earth at night
Efficiency
Light bulbs are designed to transform electrical energy into radiant (light) energy
Unfortunately, incandescent light bulbs also produce a lot of thermal energy while in use
In fact, only about 5% of the electrical energy delivered to the bulb is transformed into light energy; the rest (95%) becomes waste thermal energy
We say that the incandescent light bulb is only 5% efficient
Efficiency (copy)
Efficiency, expressed as a percentage, is
the ratio of the useful energy provided
by a device to the energy required to
operate the device
No device is 100% efficient
Thermal energy is the most common
form of waste energy
Did you know?
Throughout history many scientists have attempted to build machines that would operate for an unlimited amount of time without outside help – in other words, a perpetual motion machine
For millenia, it was not clear whether these devices were possible or not, but the development of modern theories of thermodynamics has indicated that they are possible
This is because, in order for a perpetual motion device to work, the output energy would have to be greater than the input energy (i.e. eff > 100%)
http://www.youtube.com/watch?v=tlx2PgESXhs http://www.youtube.com/watch?v=287qd4uI7-E
Efficiency
1. A firefly’s body transforms chemical energy in food into radiant energy but appears as a greenish glow in its abdomen. Fireflies use this glow to attract mates or prey. What is a firefly’s efficiency if its body transforms 4.13 J of chemical energy into 3.63 J of radiant energy?
2. A painter uses 1.93 kJ of mechanical energy to lift a 20.0 kg paint barrel to a height of 7.50 m above the ground. a) how much work was done lifting the paint barrel? b) how much energy does the paint barrel actually possess at the top? c) what is the efficiency of the rope-and-pulley system?
Improving Efficiency
A primary goal of scientists and engineers is to improve the efficiency of devices and processes that transform energy
For example, light bulbs are more efficient when they transform a greater amount of electrical energy into radiant energy
This is achieved, for example. In fluorescent and compact fluorescent lamps (CFLs)
Fluorescent lamps may transform up to 25% of the supplied electrical energy into radiant energy
This is a significant improvement in efficiency
Improving Efficiency
Fluorescent lamps, however, are not without
problems. They include the following:
1. Fluorescent lamps typically cost more than
incandescent bulbs to purchase
2. Fluorescent lamps contain mercury, a
poisonous element, which pollutes the
environment when the lamps are not
disposed of properly
Sources of Energy
We obtain energy from a variety of
sources.
Energy-rich substances such as crude oil
and natural gas are commonly called
energy resources
Some energy resources are considered
non-renewable while others are
renewable
A non-renewable energy
resource is an energy-rich
substance that cannot be
replenished as it is used
Fossil fuels make up the largest
portion of non-renewable energy
resources
A renewable energy resource is
an energy-rich substance with an
unlimited supply or a supply that
can be replenished as the
substance is used
Includes hydroelectricity and
others (solar, wind, tidal,
geothermal, biomass and fusion
Sources of Energy (copy)
Energy Resource: energy-rich substance
Non-Renewable Energy Resource: substance that cannot
be replenished as it is used (fossil fuels, nuclear energy)
Renewable Energy Resource: substance with an unlimited
supply (hydroelectricity, solar, wind, tidal, geothermal, biomass,
and fusion)
Three main sources of electrical energy production in
Ontario:
Sources of Energy – Fossil Fuels
Fossil fuels are recovered from the ground in raw form
They then undergo some form of energy transformation to make them useful
When burned directly, the fuel products can be used to operate the engines of vehicles and furnaces to heat buildings
Note: as the supply of oil and natural gas diminishes, less conventional fossil fuel resources, such as Western Canada’s tar sands, will become more important
Sources of Energy – Fossil Fuels
The fuel products can also be used to generate electricity
In this process, the fossil fuel is burned to produce a
steam, which in turn drives large turbines connected to
huge electric generators
Sources of Energy - Nuclear
Nuclear energy is a form of potential energy that is used for the generation of electricity
Uranium undergoes nuclear fission, in which the nucleus (core) of each atom splits and, in doing so, releases a relatively large amount of thermal energy
Note: the combination of smaller nuclei to form larger nuclei is called nuclear fusion, which is the power source of the sun
Sources of Energy - Nuclear
Thus, for electrical energy production, uranium serves the
same function as fossil fuels
The uranium undergoes fission to produce steam, which
in turn drives large turbines connect to huge electric
generators
Sources of Energy - Nuclear
Ontario obtains about 37% of its electricity from
generating stations using nuclear energy
Sources of Energy - Hydroelectric
The kinetic energy of rushing water is
transformed into electrical energy
(electrical current) in a hydroelectric
power plant
Electrical energy produced in this way is
called hydroelectricity or simply, hydro
Note: hydroelectric power plants produce
more electrical energy than any other
renewable energy resource in the world
Source of Energy - Hydroelectric
With a hydroelectric power plant, a dam is built to create a large reservoir of water
As water in the reservoir falls through the penstock, it gains kinetic energy and strikes the blades of turbines at the lower end
This spins the turbines which then drive huge electric generators attached to the turbines
Sources of Energy - Hydroelectric
Ontario obtains about 26% of its electricity from
hydroelectric generating stations
Sources of Energy – Comparison of…
Alternative energy sources (wind, solar…) supply the
remaining 1%
Conserving Energy – The Future
One fact is certain in Ontario: we are going to need to generate increasing amount of electrical energy far into the foreseeable future
Our population and economy are growing, which means that we will need more electricity
However, none of the renewable energy sources can currently be manufactured and operated cheaply enough to make them a viable alternative in the foreseeable future
So…. We will have to build new generating stations that use the same non-renewable energy resources as our existing generating stations
Conserving Energy – The Future
Regardless, energy may be conserved by designing, producing,
and using machines, appliances and devices that transform
energy more efficiently
Energy may also be conserved by:
Turning off lights when not required
Switching off electrical devices into of leaving them on standby mode
Taking short showers instead of baths if possible
Running dishwashers and clothes dryers only when they are full
Hanging clothes to dry
Using fans to reduce the need for air conditioning
Using public transit and car-pooling when possible
Questions
1. An article on the Internet claims, “Fossil fuels are actually a renewable energy resource since decaying plant and animal matter is making new oil, natural gas, and coal all of the time”. Discuss the validity of this statement.
This is true in the sense that they do come from decaying plant and animal matter
However, they are not renewable in the sense that the process takes millions of years to happen
2. Which alternative energy resource is most likely to be developed in your area? Explain why.
- Solar and wind