5.4 Efficiency

1. 5.4 Efficiency Have you ever noticed how hot an incandescent light bulb gets after it has been left on for a while? An incandescent bulb transforms only 5% of the electrical energy delivered to it into radiant energy. The other 95% is transformed into thermal energy. Since the intended purpose of a light bulb is illumination, not heating, the thermal energy produced is considered to be waste energy. We say that the incandescent light bulb is 5% efficient.

2. 5.4 Efficiency Efficiency, expressed as a percentage, is the ratio of the amount of usefuloutput energy produced (Eout) by a device, to the total amount of energy put into the device (Ein). No device or process is 100% efficient. Thermal energy is the most common form of waste energy. Scientists and engineers are always trying to improve the efficiency of devices and processes that transform energy. Table 1 p.244 – Energy Transformation Efficiencies of Various Devices and Processes SP # 1,2 p.242-243

3. 5.4 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. A non-renewable energy resource is a substance that cannot be replenished as it is used up in energy transformation processes. Examples include fossil fuels (coal, oil, natural gas) and nuclear energy. A renewableenergy resource is a substance with an unlimited supply or a supply that can be replenished as it is being used. Examples include hydroelectricity, solar, geothermal, wind, and tidal energies, and biofuels.

4. 5.4 Sources of Energy – Fossil Fuels Most automobile engines use the chemical energy in fossil fuels such as gasoline and diesel. Fossil fuels are produced by the decayed and compressed remains of plants and animals that lived hundreds of millions of years ago. Crude oil is pumped from underground deposits, then refined into a variety of useful substances. Fossil fuels are anon-renewable energy resource because it takes millions of years for them to form.

5. 5.4 Sources of Energy – Nuclear Energy Nuclear energy is a form of potential energy produced by interactions in the nuclei of atoms. When large unstable nuclei, such as uranium, undergo nuclear fission, its nucleus splits into smaller, more stable nuclei. As a result, a large amount of thermal energy is released. The combination of smaller nuclei to form larger nuclei is called nuclear fusion, which is the power source of the Sun.

6. 5.4 Sources of Energy – Nuclear Energy Basic operations of a Nuclear Power Plant

7. 5.4 Sources of Energy – Solar Energy A common renewable energy source is the radiant energy from the Sun, or solar energy. Solar energy may be transformed into thermal energy for heating or into electrical energy to run electrical devices and appliances. Passive Solar Design takes advantage of the Sun’s radiant energy for heating, in the design of homes and buildings, helping to reduce the need for furnaces and air conditioners. A photovoltaic cell transforms radiant energy into electrical energy.

8. 5.4 Sources of Energy – Hydroelectricity The kinetic energy of rushing water is transformed into electrical energy in a hydroelectric power plant. It produces more electricity than any other renewable resource in the world. Electrical energy produced this way is called hydroelectricity. As water in the reservoir falls through the penstock, it pushes the blades of the turbine. The turbine is connected to an electricity generator, which produces electric current.

9. 5.4 Homework • Read p.245-249 • Practice # 1,2 p.243 • Questions # 1-7 p.249