SPH3U UNIVERSITY PHYSICS

Transcription

1 SPH3U UNIVERSITY PHYSICS ENERGY & SOCIETY L & (P ) Incandescent light bulbs were invented over 150 years ago. Today, billions of light bulbs (lamps) illuminate vast areas of Earth at night. January 16, U3 - & 1 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. January 16, U3 - & 2 1

2 , expressed as a percentage, is the ratio of the useful energy provided by a device to the energy required to operate the device. E efficiency = E x 100% no device or process is 100% efficient thermal energy is the most common form of waste energy (unless it is the desired form of energy) out in January 16, U3 - & 3 DYK? 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 millennia, it was not clear whether these devices were possible or not, but the development of modern theories of thermodynamics has indicated that they are impossible. 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%). January 16, U3 - & 4 EFFICIENCY ratio of the useful energy provided by a device (i.e. E out ) to the energy required to operate the device (i.e. E in ) no device or process is 100% efficient so E in > E out E efficiency = E out in where E out E in is the useful energy output (J) is the amount of energy used (J) Thermal energy is the most common form of waste energy January 16, U3 - & 5 2

3 1. A firefly s body transforms chemical energy in food into radiant energy that 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? eff = 87.9 % January 16, U3 - & 6 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? (a) W = 1.93 kj 7 W=)E January 16, U3 - & 7 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. (b) How much energy does the paint barrel actually possess at the top? (b) E T@top = 1.47 kj January 16, U3 - & 8 3

4 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. (c) What is the efficiency of the ropeand-pulley system? (c) eff = 76% January 16, U3 - & 9 Improving 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. January 16, U3 - & 10 Improving 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. January 16, U3 - & 11 4

5 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. ENERGY RESOURCE energy-rich substance January 16, U3 - & 12 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. NON-RENEWABLE ENERGY RESOURCE substance that cannot be replenished as it is used includes fossil fuels (coal, oil, and natural gas) and nuclear energy January 16, U3 - & 13 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. RENEWABLE ENERGY RESOURCE substance with an unlimited supply or a supply that can be replenished as it is used includes hydroelectricity and others (solar, wind, tidal, geothermal, biomass and fusion) January 16, U3 - & 14 5

6 3. Although renewable energy resources are replaceable or unlimited in supply, non-renewable energy resources such as coal, oil, and natural gas continue to be the most widely used sources of energy in the world today. Why? (Hint: there are two major reasons.) Î Much of today s technology is designed to transform the chemical energy in fossil fuels into other forms of energy. Ï The large-scale, global use of fossil fuels and fossil fuel-using devices keeps their prices relatively low. January 16, U3 - & The three main sources of electrical energy production in Ontario are fossil fuel, nuclear energy, and hydroelectric. Complete a chart similar to the one below detailing the type of energy, how and how much electrical energy is produced by each and some advantages and disadvantages of each? Type How? % Pro Con Fossil Fuel Nuclear Hydroelectric January 16, U3 - & 16 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. 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. January 16, U3 - & 17 6

7 Fossil Fuels The fuel products can also be used to generate electricity. In this process, the fossil fuel is burned to produce steam, which in turn drives large turbines connected to huge electric generators. January 16, U3 - & 18 Fossil Fuels Ontario obtains about 36% of its electricity from generating stations using fossil fuels. January 16, U3 - & 19 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. The combination of smaller nuclei to form larger nuclei is called nuclear fusion, which is the power source of the Sun. January 16, U3 - & 20 7

8 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 connected to huge electric generators. January 16, U3 - & 21 Nuclear Ontario obtains about 37% of its electricity from generating stations using nuclear energy. January 16, U3 - & 22 Hydroelectric The kinetic energy of rushing water is transformed into electrical energy (electric current) in a hydroelectric power plant. Electrical energy produced in this way is called hydroelectricity or simply, hydro. Hydroelectric power plants produce more electrical energy than any other renewable energy resource in the world. January 16, U3 - & 23 8

9 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. January 16, U3 - & 24 Hydroelectric Ontario obtains about 26% of its electricity from hydroelectric generating stations. January 16, U3 - & 25 Comparison of Fossil Fuel Nuclear Hydroelectric Type C Non-renewable C Non-renewable C Renewable How? C fuel is burned C heat boils water C steam turns a turbine which turns a generator C fission of atoms C heat boils water C steam turns a turbine which turns a generator % C 36 C 37 C 26 C water is dammed C falling water turns a turbine which turns a generator Pro C easy/cheap to use C no emissions C plentiful in Ontario Con C pollution C global warming C potential for disaster C storage of spent fuel C destroys fish/wildlife habits Alternative energy sources (wind, solar,...) supply the remaining 1%. January 16, U3 - & 26 9

10 Conserving Energy The Future One fact is certain in Ontario. We are going to need to generate increasing amounts 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. And so the logical conclusion, then, is that we will have to build new generating stations that use the same nonrenewable energy resources as our existing generating stations. January 16, U3 - & 27 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 lights off when not required switching off electrical devices instead of leaving them on standby mode taking short showers instead of baths if possible running dishwashers and clothes washers 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 January 16, U3 - & 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 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. January 16, U3 - & 29 10

11 6. Which alternative energy resource is most likely to be developed in your area? Explain why. solar and wind January 16, U3 - & 30 U Check Your Learning TEXTBOOK P.249 Q.2,3 WIKI (ENERGY) O... 3U3 - QUIZ#1 (Work & Energy) January 16, U3 - & 31 11