- •Методические указания для самостоятельной работы бакалавров заочного обучения
- •Уфа – 2012
- •От автора
- •Contents
- •1 Atom is a source of energy
- •2 Energy and its forms
- •2.1 Answer the following questions
- •3 Law of conservation and transformation of energy
- •3.1 Answer the following questions
- •4 Heat is a form of energy
- •4.1 Answer the following questions
- •5 Sources of energy
- •5.1 Answer the following questions
- •6 Electric energy
- •6.1 Answer the following questions
- •7 Nuclear energy
- •7.1 Answer the following questions
- •8 Solar energy
- •9 Electricity
- •9.1 Answer the following questions
- •10 Magnets and electricity
- •10.1 Answer the following questions
- •11 Batteries produce electricity
- •11.1 Find and read all the international words in the text.
- •12 Direct current and alternating current
- •12.1 Answer the questions
- •12.2 Test. Choose the correct variant
- •13 Conductors
- •13.1 Answer the questions
- •13.2 Test. Choose the correct variant
- •14 Insulators
- •14.1. Answer the questions
- •14.2 Test. Choose the correct variant
- •15 Transmission of electric power
- •15.1 Answer the following questions
- •15.2 Choose the correct variant:
- •16 Electric lines and their efficiency
- •16.1 Complete the sentences using the correct variant
- •16.2 Answer these questions
- •17 How electricity is generated
- •18 Electric motors
- •18.1 Answer the following questions
- •18.2 Translate the following words and define their part of speech:
- •English – Russian vocabulary a
13.1 Answer the questions
Into what groups are materials divided?
What do conductors do?
What materials are common conductors?
What metals have high mechanical strength?
13.2 Test. Choose the correct variant
All materials are divided into
conductors and semiconductors
conductors, insulators and semiconductors
Copper has
high mechanical strength
low mechanical strength
Carbon has
a positive coefficient of resistance
a negative coefficient of resistance
Copper is commonly used to produce
heaters
brushes
14 Insulators
Insulating materials have a very low conductivity. They offer extremely high resistance to the flow of current. Insulators are used in electric devices to isolate conductors. Thus they should have a high dielectric strength and a high resistivity. Their mechanical properties are also important for practical use.
Insulators are divided into gaseous, liquid, solid. They are also divided into groups according to their heat resistance.
The main gaseous insulator is air. The dielectric strength of air is extremely low; it is lower than the strength of most liquid and solid dielectrics. Liquid insulators are mineral oils, synthetic liquids, resins, and others. Mineral oils are used in oil transformers, cables and capacitors. In transformers, oil is used to insulate current conducting parts. As to resins, at low temperatures they are amorphous. When heated, they become first plastic, then liquid. Resins are the most important components of many plastics. Plastics are used as wire and cable insulation. Solid insulators are paper, cloth, plastics, porcelain, and clastomers. Plastics are widely used in electrical engineering as insulating and structural materials.
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14.1. Answer the questions
What materials offer high resistance?
Where are insulators used?
What properties of insulators are important for practice?
Into what groups are insulators divided?
What is the main gaseous insulator?
What are liquid insulators?
14.2 Test. Choose the correct variant
Insulators offer
extremely high resistance
extremely low resistance
They should have
a high dielectric strength
a low electric strength
Their mechanical properties
are important for practice
are not important for practice
Commonly used insulating materials are
liquid
gaseous
solid
15 Transmission of electric power
Electric power is generated at power plants and it must be transmitted to other parts of the country. Thick wires carry electric power over long distances. The wires are not always made of copper, often they are made of other metals.
A number of wires put together form one thick cable. A cable consists of a number of wires put together and a pair consists of two insulated conductors forming a metallic circuit. Thus the basic transmission element of communications is a long transmission line. A cable is the main part of this long transmission line. Nowadays the electricity is transmitted over long distances and the length of transmitting power lines varies from area to area.
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