Учебное пособие предназначено для бакалавров всех специальностей и направлений подготовки радиотехнического факультета. В нем представлены материалы для аудиторной и самостоятельной работы
 Скачать 1.03 Mb.
|
UNIT 3Task 1. Study new words and word combinations.
Task 2. Read the text about substances and elements they consist of. All substances, solids, liquids or gases, are composed of one or more of the chemical elements. Each element is composed of identical atoms. Each atom is composed of a small central nucleus consisting of protons and neutrons around which orbit shells of electrons. These electrons are very much smaller than protons and neutrons. The electrons in the outermost shell are called valence electrons and the electrical properties of the substance depend on the number of these electrons. Neutrons have no electric charge, but protons have a positive charge while electrons have a negative charge. In some substances, usually metals, the valence electrons are free to move from one atom to another and this is what constitutes an electric current. TASK 3. Read the text again and complete the sentences with the missing information. 1. Elements make up …. 2. Identical atoms …. 3. Atoms consist of …, … and …. 4. Inside there are … and …, while outside …. 5. Shells …. 6. Valence electrons …. 7. Neutrons do not have …. 8. Electricity is generated when …. TASK 4. Listen and complete the text with the missing information. Electricity consists of a 1) … of free electrons along a conductor. To produce this current flow, a generator is placed at the end of the conductor in order to move the 2) …. Conductors Electricity needs a material which allows a current to pass through easily, which offers little 3) … to the flow and is full of free electrons. This material is called a conductor and can be in the form of a bar, tube or sheet. The most commonly used 4) … are wires, available in many sizes and thicknesses. They are coated with insulating materials such as plastic. Semiconductors Semiconductors such as silicon and germanium are used in transistors and their conductivity is halfway in between a conductor and an 5) …. Small quantities of other substances, called impurities, are introduced in the material to 6) … the conductivity. Insulators A material which contains very 7) … electrons is called an insulator. Glass, rubber, dry wood and 8) … resist the flow of electric charge, and as such they are good insulating materials. TASK 5. Read the text again and decide if the following statements are true (T) or false (F), then correct the false ones. 1. A flow of electrons moving inside a conductor creates an electric current. 2. A generator is used to move the charges. 3. Electrons can easily pass through any material. 4. Any material is a good conductor. 5. Conductors are coated with insulators. 6. The presence of free electrons affects the conductivity of materials. 7. Impurities are introduced to increase conductivity. 8. Insulating materials resist the flow of electrons. TASK 6. Read the text and complete the table with the missing information. There are two types of current: Direct current (DC) and Alternating current (AC). Direct current is a continuous flow of electrons in one direction and it never changes its direction until the power is stopped or switched off. Alternating current constantly changes its direction because of the way it is generated. The term 'frequency' is used to indicate how many times the current changes its direction in one second. Alternating current has a great advantage over direct current because it can be transmitted over very long distances through small wires, by making energy high voltage and low current. There are several quantities that are important when we are talking about electric current. Volts (V) – so named after the Italian physicist Alessandro Volta – measure the difference of electric potential between two points on a conducting wire. Amperes (A) measure the amount of current flowing through a conductor, that is to say the number of electrons passing a point in a conductor in one second. Coulomb (C) measure the quantity of charge transferred in one second by a steady current of one ampere. Power is the rate at which work is performed and it is measured in watts (W). A Kilowatt (kW), which is equal to one thousand watts, is used to measure the amount of used or available energy. The amount of electrical energy consumed in one hour at the constant rate of one kilowatt is called kilowatt-hour.
TASK 7. Listen to the recording and fill in the gaps. The position of Vanessa Thompson is 1)…. The lecture is read on 2)… and 3)….The students learn about 4)… in her class. The first thing the students study is how 5)…. This is important for in-depth study of 6)…. The three things which students learn about after that are 7)…, 8)… and 9)…. Students also learn how substance 10)…. In the end, they are explained how to 11)… electricity. The units of measurement which they study are amperes, 12)…, 13)…, and 14)…. Finally students do a 15)… which is an electrical 16) …. |