The sources of heat
Nuclear energy can produce great quantities of heat Nuclear weapons release so much heat so quickly that they destroy everything around them. Their heat cannot be put to useful work. But in a device called a reactor, heat can be produced from nuclear energy slowly enough to generate electricity and to do other jobs.
Friction. When one object rubs against another, heat is produced. Friction is usually an unwanted source of heat because it may damage objects. In a machine, for example, the heat created as the moving parts rub against one another may cause those parts to wear down. For this reason, oil is used between moving machinery parts. The oil reduces friction and so decreases the generation of heat.
Electricity. The flow of electricity through metals, alloys, and other conductors (substances that carry electric current) generates heat. People make use of this heat in the operation of many appliances, including electric furnaces, ovens, ranges, dryers, heaters, toasters, and irons.
These units store the heat until daytime, when it can be used to maintain comfortable room temperatures without the use of additional electricity.
Electric heat is clean for the homeowner. But the power plants that generate the electricity must burn about three units of energy for every one unit that is delivered to the home. In addition, the increased use of electricity for heating and other uses requires the construction of more power plants.
Many engineers believe it is more efficient for homes to burn fuel for heat than to produce electricity for heating. These experts point out that the best power plants change only about 30 to 40 per cent of the energy they use into electricity. A gas or oil heating system can deliver more than 60 per cent of the energy it consumes as heat A heat pump driven by gas or oil can collect enough additional heat energy from external sources so that it delivers 1 1/2 times the energy it uses.
Gas produces heat with little air pollution. Nearly all the gas used for heating homes in the United States and Canada is natural gas or LPG (liquefied petroleum gas). Natural gas comes from underground rock formations as does oil. Most natural gas reaches homes through pipelines. Gas is simple to burn. A gas furnace pipes the fuel to burners that ignite it
Since the early 1970s, certain areas of the United States have experienced occasional shortages of natural gas. Such shortages have resulted from an increased demand for gas and decreased domestic reserves of the fuel. Unequal distribution of gas to different parts of the country has contributed greatly to the problem.
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Oil Coal for heating is available in several grades, depending on its heating capability and sulfur content. Local trucks deliver the oil to homes, where it is stored in tanks until used. A home oil furnace has either a pot type or a gun type burner. In a pot type burner, the fuel oil flows into a shallow depression in the bottom of the furnace. In a gun type burner, the oil is sprayed through a nozzle under air pressure. The burner uses an air pump to vaporize the fuel. The added air makes the oil burn more efficiently.
Heating oil has been widely used in the United States since the 1940`s. However, U.S. petroleum reserves have become too scarce to meet the continued high demand, resulting in a dependence on imported oil. Because of this situation, shortages of heating oil have occurred whenever political disturbances in oil-producing countries reduced the availability of foreign oil. For example, the revolution in Iran in 1979 disrupted the flow of oil from that country and caused a temporary shortage of heating fuel in the United States.
Coal for heating is available in several grades, depending on its heating capability and sulfur content. The two most common types of coal burned in the United States are anthracite (hard coal) and bituminous (soft coal). Anthracite produces less smoke and sulfur dioxide when burned than does bituminous coal. As a result, anthracite causes less pollution. But most of the coal deposits in the United States are bituminous.
1.Study the following words:
Device, friction, release, wear down, reduce, decrease, alloy, external sources
Ignite, shortages, bituminous, nozzle, conductors, shortage.
2. Define the part of the speech of the following words:
Pipeline, decrease, resulting, less, efficiently, availability, until, anthracite, capability, whenever, additional, driven
3. Complete the sentences with appropriate words from the text:
a) Most natural gas ….. homes through pipelines.
b) ….for heating is available in several grades, depending on its heating capability and sulfur content.
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c) The burner uses an … … to vaporize the fuel.
d) A home oil furnace has either a…….or a ….. burner.
e)....produces heat with little air pollution
4. Give the English definitions of the following words:
Coal, tanks, friction, alloys, shallow, deposits, homeowner
5. Put questions to the following sentences:
a) People make use of this heat in the operation of many appliances, including electric furnaces, ovens, ranges, dryers, heaters, toasters, and irons.
b) These experts point out that the best power plants change only about 30 to 40 per cent of the energy they use into electricity.
c) Anthracite produces less smoke and sulfur dioxide when burned than does bituminous coal.
d) A gas furnace pipes the fuel to burners that ignite it
Text 4
What heat does.
Changes in temperature are one of the most common results when heat flows into or out of an object. The amount of heat needed to raise the temperature of one gram of a substance one degree Celsius is called the specific heat capacity of the substance. Specific heat capacity is often called simply specific heat. Scientists use the specific heat of water, which is given a value of 1, as the standard for figuring the specific heat of all other substances.
You can find out how much the temperature of a substance will rise when heat flows into it if you know how much mass (amount of matter) the substance has and what the specific heat of the substance is. First, multiply the mass by the specific heat of the substance. Then, divide the result into the amount of heat added. For example, if 10 calories of heat flow into one gram of water, how much will the temperature of the water rise? One gram multiplied by a specific heat of 1 equals 1. One divided into 10 calories equals a rise of 10 degrees Celsius.
Two substances with the same mass but different specific heats require different amounts of heat to reach the same temperature. The temperature of a substance with a low specific heat will increase more than that of a substance with a high specific heat if both substances receive the same amount of heat For example, it takes 10 calories of heat to raise one gram of water 10 degrees Celsius. But 10 calories will raise the temperature of one gram of copper 111 degrees. Copper has a low specific heat of 0.09, compared with water's specific heat of 1.
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Changes in size. As we have seen, when heat flows into a substance, the motion of the atoms or molecules in the substance increases. As a result of their increased motion the atoms or molecules take up more space and substance expands.
The opposite occurs when heat flows out of a substance. The atoms or molecules move more slowly. They therefore take up less space, and the substance contracts.
All gases and most liquids and solids expand when heated. But they do not expand equally. If a gas, a liquid, and a solid receive enough heat to raise their temperatures the same amount, the gas will expand most, the liquid much less, and the solid the least.
Thermometers, thermostats, and many other devices work on the principle of expansion and contraction. Many thermometers contain a liquid, such as alcohol or mercury, that expands and contracts evenly as the t changes. A rise or fall in temperature causes the volume of the liquid to expand or contract only slightly. But by making the liquid occupy a narrow glass tube, the liquid column moves enough so the temperature change can be seen.
Changes in temperature also cause the materials that are used in bridges, buildings, and other structures to expand and contract. This expansion and contraction can cause serious problems if the builders do not allow for it. For example, the steel beams used in a building will bend or break if they do not have room to expand. For this reason, structures have expansion joints, which allow extra space for the materials to expand and contract without damage when the temperature changes.
Engineers can determine how much the length of any material will increase when its temperature rises if they know the coefficient of linear expansion of the material. The coefficient of linear expansion indicates how much longer each meter of the material will become if its temperature increases by one degree. For aluminum, it is 0.000023. Thus, each meter of an aluminum bar become; 0.000023 of a meter longer with each degree Celsius increase in its temperature.
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1.Study the following words:
Specific heat capacity,expansion joints, copper, take up, liquid, mercury, bend,
Therefore, the motion, flow, solid
2. Complete the sentences with appropriate words from the text:
a) Celsius is called the … ….. …. of the substance.
b) Two substances with the same mass but different specific heats require different ….. to reach the same temperature.
c) Many …. contain a liquid, such as alcohol or mercury.
d) They therefore take up less … and the substance contracts.
e) Thus, each meter of an aluminum bar become; …. of a meter longer with each degree Celsius increase in its temperature.
3.Insert necessary prepositions:
a) Two substances … the same mass but different specific heats require different amounts … heat to reach the same temperature.
b) Thermometers, thermostats, and many other devices work … the principle of expansion and contraction.
c) … aluminum, it is 0.000023.
d) The steel beams used … a building will bend or break if they do not have room to expand.
4. Ask the questions:
a) The atoms or molecules move more slowly.
b) Changes in temperature also cause the materials that are used in bridges, buildings, and other structures to expand and contract.
c) All gases and most liquids and solids expand when heated.
d) This expansion and contraction can cause serious problems if the builders do not allow for it.
e) But they do not expand equally.
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