Insulators
A material which contains very few electrons is called an insulator. Glass, rubber, dry wood and plastic resist the flow of electric charge, and as such they are good insulating materials.
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.
Text 4.3
Read and translate the text.
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.
Complete the table with the missing information.
Unit of measurement |
What does it measure? |
(1) |
the number of electrons passing a given point in a conductor in one second |
(2) |
the quantity of electricity transferred by a steady current of one ampere |
(3) |
the amount of electric energy used |
(4) |
the difference of potential between two points on a conductor |
(5) |
rate at which work is done |
3 Семестр
Unit 5
Electric circuits
Text 5.1
Read and translate the text.
An electric circuit or network is a pathway through which the electric current can flow. A simple circuit consists of a power source, two conducting wires, each one attached to a terminal of the source and a device through which electricity can flow. This device is called a load and it's attached to the wires. If all the parts are properly connected, the current flows and the lamp lights up. This kind of circuit is called 'closed'.
On the contrary, if the wires are disconnected the circuit is called 'open' or 'broken'. The circuit can be opened and closed by a device called a switch.
Loads can turn electrical energy into a more useful form. Some examples are:
■ light bulbs, which change electrical energy into light energy;
■ electric motors, which change electrical energy into mechanical energy;
■ speakers, which change energy into sound.
The source provides the electrical energy used by the load. It can be a storage battery or a generator. The switch interrupts the current delivered to the load by the source and allows us to control the flow.
When an abnormally high amount of current passes through a network, you get a short circuit. This may occur when there is a drop in the resistance or a broken insulation. In order to prevent short circuits, it is best to use fuses, which melt when too much current flows through them, interrupting in this way the circuit
Match the words with their definitions.
load а a device which interrupts the circuit
switch b a circuit in which wires are disconnected
source с a device which provides power
fuse d a complete circuit with no breaks at all
closed circuit e a device which consumes electric power
broken circuit f a protective device
Read the text again and answer the following questions.
1 What does a simple circuit consist of?
2 What happens to the lamp in a closed circuit?
3 Can you name some examples of loads?
4 What is a generator?
5 What is the function of a switch?
6 When does a short circuit occur?
7 What can we use to prevent short circuits?
8 How does a fuse work?
Text 5.2
Read and translate the text.
The components of a circuit can be wired in two different ways: series or parallel.
If components are arranged one after another to form a single path between the terminals and the components, the circuit is known as a series circuit. In this type of circuit, the current flows from the negative terminal to the positive terminal, passing through all the other components of the circuit. This means that the amount of energy passing through all the components in the series is the same. The main disadvantage of a series circuit is that when a single component in the path burns out, the entire circuit stops operating (e.g. Christmas tree lights).
A parallel circuit consists of several paths connecting the different components. Each separate path is called a branch of the circuit. Current from the source divides and flows through the different branches. Unlike series circuits, if one of the components in the parallel circuit burns out, the other paths continue to operate. Parallel circuits are commonly used to connect appliances at home, so that each socket can function independently. For example, you don’t have to turn on the light in your room for the TV socket to work.
Text 5.3
Read and translate the text.
A fuse can be added to an electric circuit to protect it from the effects of undue power. This safety device, which is made of a heat-sensitive alloy, is connected in series with the circuit it has to protect. If an excessive amount of current flows through the circuit, the alloy will liquefy and open the circuit. A circuit breaker is fundamental in a house to protect circuits against overloading, overheating and short circuits. The advantage of a circuit breaker is that it can be reset after the overloading by replacing the fuse. A professional electrician should always provide his customers with a map of the electric circuit in the house so that it will be easier to work on it in case of faults.
Find synonyms for the words below.
Excessive:
Reacting to high temperatures:
To melt:
Loading up:
Adjusted:
Clients:
How energy is produced
Unit 6
Text 6.1
Read and translate the text.
Conventional power plants
Nuclear power plants
About 10% of the world's electric power is produced by nuclear power plants. Nuclear power requires little fuel and causes much less air pollution than other power plants, but it can cause severe health and environmental problems when accidents occur, with a consequent release of radioactive material. This type of energy is produced by the splitting of atoms of uranium, which releases heat. This process - called fission - produces large amounts of steam, which is used to turn the blades of turbines thus creating energy. The main problems with nuclear power are linked to the location of the power plants, as people are not willing to have these plants near their homes, and the disposal of waste material, which stays radioactive for centuries.
Thermoelectric power plants
They provide about 2/3 of the world`s electricity. This plants burn fossil fuels, such as coal, oil or natural gas, which are all non renewable resources. This means that in the future there will be a limited supply of these resources. The main advantage of thermoelectric power plants is that they are reliable and can meet the demand in peak periods. Electricity is generated by heating water in a boiler to create steam, which is then pressurized and used to turn the blades of giant turbines that produce electricity. These power plants cause environmental pollution because of the combustion of fossil fuels which release carbon dioxide.
Hydroelectric power plants
The energy produced by water can be captured and turned into electricity. The use of a dam on a river allows hydroelectric power plants to store water in an artificial lake, or reservoir. When released, the force of the water spins the blades of giant turbines, which are connected to a generator producing energy. Hydropower is one of the most important renewable energy resources, because it is reliable, efficient and does not pollute the air. Although it has high initial costs, it is cheap to operate. Unfortunately, it has a great impact on the environment, as humans, animals and plants may lose their natural habitats.
Read the texts again and decide if the following sentences are true (T) or false (F), then correct the false ones.
1 Nuclear power plants do not produce air pollution at all.
2 Accidents in nuclear power plants can have terrible consequences for the environment.
3 Nuclear power plants produce biodegradable waste material.
4 Thermoelectric power is generated by the combustion of renewable resources.
5 Thermoelectric power plants are environmentally friendly.
6 Dams are built on rivers to store water.
7 The water released from the reservoir flows through the generator.
8 The only disadvantage of hydropower is its high initial cost
Text 6.2
Alternative power sources
Read and translate the text.
Environmental problems such as the greenhouse effect and air pollution have led scientists to find alternative power sources which are renewable and less polluting.
SOLAR ENERGY
Sunlight can be directly converted into electricity by solar cells made of silicon. When light strikes the cells, a part of it is absorbed by the semiconductor material. The energy of the absorbed light knocks electrons loose, allowing them to flow freely and produce electricity. The process of converting light (photons) into electricity (voltage) is known as the photo-voltaic process (PV). Solar cells are usually combined into panels and grouped into arrays. Even if the initial costs can be high, the PV system provides an independent, reliable electrical power source. It can produce energy for more than 15 years and its routine maintenance is simple and cheap.
WIND ENERGY
Wind energy is one of the cheapest renewable technologies available today. The wind turns the blades of giant turbines, producing in this way kinetic energy which is then converted into mechanical power and electricity by a generator. The main disadvantage of wind energy is that there are few suitable wind sites where it is possible to have a constant production of electricity.
TIDAL ENERGY
This alternative power source, which is typically used in coastal areas, turns the potential energy of tides into electricity. Tidal power generators use rising and fallingtides in much the same manner as hydroelectric power plants. Large underwater turbines are placed in areas with high tidal movements and are designed to capture the kinetic energy of rising and falling tides. The turbines are driven by the power of the sea both when the tide comes in and when it goes out. The problem with tidal power is that only massive increases in tides can produce energy and there are very few places where this occurs. Moreover, the aquatic ecosystem and the shoreline can be damaged by the changes in the tidal flow.
GEOTHERMAL ENERGY
In the past, people used hot springs for bathing, cooking and heating. Geothermal energy is based on the fact that the Earth is hotter below the surface. The hot water which is stored in the Earth can be brought to the surface and used to drive turbines to produce electricity or it can be piped through houses as heat. This energy is cheap and has a low impact on the environment, but there are few sites where it can be extracted at low cost.
BIOMASS ENERGY
Biomass is a renewable energy source deriving from plant material and animal waste. When it is burnt, it releases its chemical energy as heat. Biomass fuels include forest residues (such as dead trees, branches and tree stumps), straw, manure and even municipal solid waste. Biomass energy is a natural process, it is carbon neutral and has low initial costs. It used to be the main source of heating at home in the past and it continues to be highly exploited in the developing world. The main disadvantage of biomass is that it has a smaller potential than other energy sources and requires excellent maintenance skills
Complete the table with the missing information.
Type of energy |
How it works |
Advantages |
Disadvantages |
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high initial costs |
Wind energy |
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It is a natural process because it exploits the potential energy of tides. |
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Match the words with their definitions.
1 array a - a spot where hot water comes up naturally from the ground
2 kinetic b - unwanted material left after using
3 tide с - a group of things arranged in a particular way
4 hot spring d - waste material from animals used as fertiliser
5 to pipe e - the process of keeping something in good condition by regularly checking it
6 manure f – produced by motion
7 waste g – to send a liquid or a gas through a tube
8 maintenance h – the regular change in the level of the sea caused by gravitational attraction of the moon and the sun
Text 6.3
Read and translate the text.
Electricity distribution is the final stage in the delivery of electricity to end users. In order to be able to use electric power for our daily activities, electricity must be transmitted from the power plants to other areas where it can be distributed to different consumers.
The electricity generated by power plants is increased or stepped up at substations and distributed though high- voltage transmission lines, in order to minimize energy losses and to economise on the material needed for conductors. Transmission lines use voltages as high as 765,000 volts and they are usually connected in a network. This means that if a station receives an unexpected demand for electric power, it can call on the other stations to help to meet the demand. Then electrical power is converted from high voltage to lower voltages thanks to step-down transformers which turn electricity into different power levels. Once it is sent to your neighbourhood, another small transformer mounted on a pole converts the power to even lower levels to be used at home. The final voltage is between 110 volts - for lights, TVs, and other smaller appliances - and 240 volts for larger appliances.
Reorder the different stages in the distribution system and match them to the numbers in the picture.
a □ Transmission lines carry high-voltage electricity to different substations.
b □ Electricity leaves the power plant.
с □ Electricity is stepped down by transformers.
d □ Current at lower voltages is transmitted to homes and offices.
e □ The voltage is increased at a step-up station.
f □ Power levels are lowered by small transformers mounted on poles.
Read the text again and match each sentence with its ending.
1 Power plants generate a convert electricity from high voltage levels to lower levels.
2 Transmission lines are used b - in case of an expected demand for electric power.
3 High voltages mean с - a reduction in energy losses during transmission.
4 Step-down transformers d - power and distribute it to substations.
5 Substations can help each other e - can be safely used in businesses and homes.
6 The current transmitted by poles f - to distribute high-voltage electricity to a network of substations.