CHAPTER 3. STATIC AND “CURRENT” ELECTRICITY. SERIES AND PARALLEL CONNECTIONS (СТАТИЧЕСКОЕ И ДИНАМИЧЕСКОЕ ЭЛЕКТРИЧЕСТВО. ПОСЛЕДОВАТЕЛЬНЫЕ И ПАРАЛЛЕЛЬНЫЕ СОЕДИНЕНИЯ)
Exercise 1. Read and translate the text, using the words below.
Electricity manifests itself in two seemingly different ways. They are different manifestations of the same thing. "Static" electricity was known to the ancients. It involves very high voltages and very low currents—the currents are so low that one doesn't always realize how high the voltage is. In order for such high voltages to persist somewhere, the insulation must be extremely good, that is, the resistances must be extremely high. Fortunately for the history of science, materials like glass, amber, and some types of rubber and other materials, have the necessary high resistance. (The word "electricity" comes from the Greek word for amber.)
The voltages involved with static electricity are high enough to make the leaves of an electroscope move, but the currents are so low that we would normally not notice any effect of the current. "Current" electricity involves lower voltages and currents large enough to power light bulbs, motors, and such. Rubbing a glass rod with a piece of silk can't come anywhere near to providing the required level of sustained current. To get the required sustained levels of current requires either ongoing chemical reactions (as in a battery) or electromechanical devices (as in a generator.) The ability to do this was discovered in the 18th and 19th centuries by Luigi Galvani, Alessandro Volta and Michael Faraday 
Schematic diagram showing series and parallel connections.
If we were to stack three hydroelectric dams on top of each other (that is, make the reservoir three times as deep), the pressure at the bottom would be three times as great, and the energy obtained per liter of water would be three times as great. (Or, equivalently, we make an old-fashioned water wheel with three times the vertical drop.) The electrical equivalent of this is the series connection, or the placement of electrical components in series. The voltage difference across components connected in series is the sum of the voltage differences across the individual components, but the current is the same through each component.
If we were to place three hydroelectric dams next to each other (that is, just triple the flow of water), the pressure would be the same, so the amount of energy per liter would be the same, but the overall flow of water would be three times as great, so the total power would be three times as great. The electrical equivalent of this is the parallel connection, or the placement of electrical components in parallel. The total current through components connected in parallel is the sum of the currents through the individual components, but the voltage difference is the same.
The diagram shows a simple flashlight, with two batteries connected in series and three light bulbs connected in parallel. The total voltage across the pair of batteries is 3 volts, and the current through each is 1.2 amperes. The light bulbs are connected in parallel. The voltage across each is 3 volts, and the current through each is 0.4 amperes. Each battery provides 1.8 watts of power (1.5 volts times 1.2 amperes), so both batteries combined provide 3.6 watts. Each light bulb has 0.4 amperes flowing through it, so it consumes 1.2 watts. The three bulbs in combination consume 3.6 watts.
This is an example of a schematic diagram—an abstract diagram showing how electrical components are interconnected. You could not possibly build a satisfactory house, automobile, or telescope from such an abstract description ("build roof; place on top of walls"). But electricity, passing through wires from one component to another, is so well behaved that, for ordinary electrical projects, a schematic diagram is all you need. Schematic diagrams ("schematics") are the principal workhorse of electrical engineering.
The terms "series" and "parallel" are actually used quite loosely by electrical engineers, to describe aspects of circuit topology. For example, the flashlight depicted above lacks an on-off switch. One would put the switch in series with the parallel assemblage of light bulbs.
Words to be remembered.
manifestation–проявление
rod–прут; шток; стержень
to stack –складывать в стог
to triple–утраивать
flashlight–электрический фонарь
to consume–потреблять
to depict–изображать, изобразить
bulb–электрическая лампочка
Exercise 2. Answer the following questions.
1. What do you know about “static” electricity?
2. What materials have high resistance?
3. What can you say about “current” electricity?
4. Can you describe the series connection?
5. What about parallel connection?
6. What does the diagram show?
7. The light bulbs are connected in parallel, aren`t they?
8. Will a schematic diagram be enough for ordinary electrical projects?
9. What is used to describe aspects of circuit topology?
10. What does the flashlight depicted above lack?
Exercise 3. Learn the following word combinations.
Glass road, sustained current, chemical reactions, electromechanical devices, hydroelectric dams, electrical equivalent, overall flow, total power, light bulbs, series connection, parallel connection.
Exercise 4. Make up your own sentences, using word expressions from ex. 3.
Exercise 5. Translate the following sentences from Russian into English.
1. Электричество проявляет себя двумя разными способами. 2. Статическое электричество было известно ещё древним. 3. Такие материалы как стекло, янтарь, некоторые виды резины и другие имеют необходимое сопротивление. 4. Слово «электричество» происходит от греческого слова янтарь. 5. Рисунок изображает простой фонарик с двумя батарейками, соединёнными последовательно и тремя лампочками, соединёнными параллельно. 6. Схемы – это основополагающее электротехники. 7. Фонарику недостаёт выключателя. 8. Схема показывает, как электрические детали соединены между собой.
Exercise 6. Match Russian and English terms in columns A and B.
A:device, manifestation, dam, bulb, circuit, flashlight
B:дамба, цепь, устройство, фонарик, проявление, лампочка.
Exercise 7. Match the two parts of the sentences.
1. “Static” electricity was known to …
a) the ancients
b) the ancestors
c) modern people
2. Materials like glass, amber, and some types of rubber have the necessary …
a) medium resistance
b) low resistance
c) high resistance
3. To get the required sustained levels of current requires either ongoing chemical reactions or …
a) mechanical devices
b) electromechanical devices
c) electrical devices
4. The diagram shows a simple flashlight, with two batteries connected in series and three light bulbs connected …
a) in parallel
b) in series
c) on the contrary
5. Schematic diagrams are the principal …
a) workhorse of electromechanics
b) workhorse of electrical engineering
c) workhorse of electrotechnics
6. The terms “series” and “parallel” are actually used quite loosely by electrical engineers, to describe …
a) aspects of individual components
b) aspects of schematic diagrams
c) aspects of circuit topology
7. One would put the switch in series with the …
a) series assemblage of light bulbs
b) parallel assemblage of light bulbs
c) parallel assemblage of flashlights
8. The word “electricity” comes from …
a) the English word for lightning
b) the Latin word for light
c) the Greek word for amber
CHAPTER 4. OHM`S LAW, JOULE`S LAW, KIRCHHOFF`S LAWS (ЗАКОН ОМА, ЗАКОН ДЖОУЛЯ, ЗАКОНЫ КИРХГОФА)
Exercise 1. Read and translate the text, using the words below.
We use the hydraulic analogy one last time. If we increase the pressure of water going into a pipe, the flow will increase. The flow will be roughly proportional to the pressure. For wider pipes, the proportionality constant will be different than for narrower pipes.
There is a similar principle for electricity: Ohm's law, discovered by Georg Simon Ohm in the 1820's, states that the current through a resistive medium is proportional to the applied voltage. Whereas the linearity of water flow and pressure is only approximate, Ohm's law is extremely accurate for virtually all substances of interest, other than things that make use of special semiconductor properties. The proportionality constant, for a given device, is the resistance, measured in ohms. Ohm's law is:
Voltage equals current times resistance.
Also stated, of course, as:
Simple analysis of series and parallel connections (a long wire is equivalent to two shorter wires in series; a thick wire is equivalent to two thinner wires in parallel) shows that the resistance of an object made of some substance is proportional to the length and inversely proportional to the cross-sectional area. One can therefore see that the proper measure of the resistivity of a substance is "ohm meters". This is a somewhat non-intuitive way of expressing something, and a more common way is to measure the conductivity, which is the reciprocal of resistance, in siemens per meter.
Electrical resistivity varies by over 20 orders of magnitude between metals and air, and over 30 orders of magnitude between metals and various insulating materials. This is why it is possible to send telephone and other cable communications through many miles of wire, where the wire thickness is a fraction of a millimeter, with virtually no leakage between adjacent wires.
Here are a few approximate conductivities:
· Superconductors: infinity (because of complicated quantum-mechanical phenomena)
· Silver: 6 * 107
· Silicon: 2 * 10-3 (but, in semiconductor materials, it is "doped" with impurities, giving it a much higher conductivity)
· Glass: about 10-12
· Air: about 10-14
· Paraffin: about 10-17
· Teflon: about 10-23
Electrical devices that are intended to exhibit resistance are resistors. They are manufactured in resistances from a small fraction of an ohm to many megohms.
From what we know about ohm's law, and about voltages and currents in series and parallel connections, we can derive the rules for resistors in series and parallel:
When resistances of 
and 
are placed in series, the resultant resistance is 
When resistances of and are placed in parallel, the resultant resistance is 
One sometimes encounters phrases like "I-squared-R losses" in a wire. This is a combination of the power formula and Ohm's law.
Notice that the amount of power lost in a wire is proportional to the square of the current.
The phenomenon of heat being evolved when electricity passes through a conductor is sometimes called Joule's law. It's really just a consequence of conservation of energy and the equivalence of heat to other forms of energy.
There are two famous "laws" of electrical engineering, known as Kirchhoff's Voltage Law and Kirchhoff's Current Law. They are really just straightforward applications of what has been discussed above.
Kirchhoff's Voltage Law (sometimes abbreviated KVL): The sum of the voltage drops around any closed path in a circuit is zero. This is just conservation of energy – a quantity of electric charge could pick up energy for free by going around a closed loop with a nonzero total voltage drop. Remember that "voltage drop" between two points can be either positive or negative.
Kirchhoff's Current Law (sometimes abbreviated KCL): The sum of the currents flowing into a point in a circuit is zero. This is just conservation of charge. Remember that current flow "into" a point is negative if the current is flowing out.
Words to be remembered.
reciprocal–взаимный, обоюдный; эквивалентный
magnitude–величина; размеры; важность
inverse–обратный, перевёрнутый
fraction–дробь; частица
linearity–линейность
loop–закреплять петлёй
Exercise 2. Answer the following questions.
1. What will happen if we increase the pressure of water going into a pipe?
2. Is there a similar principle for electricity? What is it?
3. What does simple analysis of series and parallel connections show?
4. How does electrical resistivity vary?
5. Why is it possible to send telephone and other cable communications through many miles of wire?
6. What is a resistor?
7. What is proportional to the square of the current?
8. What is called Joule`s law?
9. What is the sum of the voltage drops around any closed path in a circuit?
10. Can “voltage drop” between two points be either positive or negative?
Exercise 3. Match the words on the left with the words on the right.
| 1. roughly proportional | 1. прямое применение |
| 2. resistive medium | 2. изоляционные материалы |
| 3. applied voltage | 3. прямо пропорционально |
| 4. semiconductor properties | 4. толщина провода |
| 5. inversely proportional | 5. способ сопротивления |
| 6. insulating materials | 6. применяемое напряжение |
| 7. wire thickness | 7. сохранение энергии |
| 8. adjacent wires | 8. свойства полупроводника |
| 9. conservation of energy | 9. обратно пропорционально |
| 10. straightforward application | 10. смежные провода |
Exercise 4. Translate the following sentences from Russian into English.
1. Если мы увеличим давление на воду, проходящую по трубе, то поток увеличится. 2. Поток будет прямо пропорционален давлению. 3. Простой анализ последовательных и параллельных соединений показывает, что сопротивление объекта пропорционально его длине и обратно пропорционально поперечному сечению. 4. Поэтому можно разговаривать по телефону через большое расстояние . 5. Из того, что мы знаем о законе Ома, можно вывести правила для последовательных и параллельных резисторов. 6. Тепловое явление, связанное с электричеством, проходящим через проводник, иногда называют законом Джоуля. 7. На самом деле, это просто последствие сохранения энергии. 8. Помните, что «падение напряжения» между двумя точками может быть как положительным, так и отрицательным.
Exercise 5. Complete the sentences.
1. If we increase the pressure of water going into a pipe … 2. … the proportionality constant will be different than for narrower pipes. 3. Ohm`s law states that … 4. … is the resistance, measured in ohms. 5. Simple analysis of series and parallel connections shows that … 6. … are resistors. 7. The amount of power lost in a wire is … 8. … is sometimes called Joule`s law. 9. It`s really just a consequence of conservation of energy and … 10. There are two famous “laws” of electrical engineering, known as …
Exercise 6. Tell what you have learnt about:
a) Ohm`s law
b) resistors
c) “I- squared-R losses”
d) Joule`s law
e) Kirchhoff’s Voltage law
f) Kirchhoff’s Current law.