Efficiency & Sources of Energy

Pg. 242 - 249

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

Ontarians obtain about 36% of its electricity from

generating stations using fossil fuels

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

Textbook

Page 249, #2 , 3

Time for a QUIZ!!! (Work & Energy)