Series and Parallel Connections

There are two basic types of circuits: series and parallel. In a series circuit the components of the circuit are arranged in such a way that they are connected end to end, so that the entire current passes through each component without division or branching into parallel circuits. You should know the difference between series and parallel connections in circuits.

S eries connections. A series circuit is a complete circuit that has more than one electrical load through which the current has to flow. So, components that are connected one after another on the same loop of the circuit are connected in series. The current flows through all the components one after the other. The circuit diagram (Fig. 1) shows a circuit with two lamps connected in series. If one lamp breaks, the other lamp will not be lit. Fig. 1. Two lamps connected in series.

It is necessary to remember the characteristics of the current and potential difference in series circuits.

When two or more components are connected in series, the same current flows in each component and the total potential difference of the supply is shared between them. This means that if you add together the voltages across each component connected in series, the total equals the voltage of the power supply.

The total resistance in such a circuit is the sum of the resistances of individual components. Two identical resistors connected in series will share the potential difference. They will get half each. For example if two identical resistors are connected in series to a 3 V cell then the potential difference across each of them is 1.5 V. If resistors connected in series are not the same then the potential difference is larger across the larger of the resistors. For example if a 2 Ω and a 1 Ω resistor are connected in series to a cell of 3V, then the potential difference across the 2 Ω resistor will be 2 V, and across the 1 Ω resistor will be 1 V. If there is a change in the resistance of one component then this will result in a change in the potential differences across all of the other components in the circuit.

Wiring in series is satisfactory if the devices need only low amounts of power for operation since each added resistor will cause the current in circuit to drop.

P arallel connections. A parallel circuit is a complete circuit where the current flow has more than one electrical path for the current flow. In parallel circuits the electric current flows through different pathways. Each branch of such a circuit can be switched on or off independently. This allows the use of some or all of the components by choice. The diagram (Fig. 2) shows a circuit with two lamps connected in parallel. If one lamp breaks, the other lamp will still be lit. Because a parallel circuit has more paths for charges to flow along, the current is bigger, and the resistance of the whole circuit is smaller. Fig. 2. Two lamps connected in parallel.

All parallel circuits have the following characteristics. When two or more components are connected in parallel, the total current flowing in the circuit is shared between the components and the potential difference across them is the same. This means that if a voltage across a lamp is 12 V, the voltage across another lamp connected in parallel is also 12 V.

The total resistance of all components in parallel wiring is less than the resistance of any one of them. The more branches are available in parallel wiring, however, the lower the total resistance in the circuit becomes, and thus, the higher the total current. The total current that flows into the branches will equal the sum of the current in each branch.

In addition to the advantage of using resistors along each branch independently, the parallel scheme of wiring allows the addition of extra branches without changing the current in the branches already in use, thus keeping the energy consumption in each branch unchanged. In the house each additional device that is plugged into a given circuit adds another parallel branch. But with each device added, the total resistance drops and the total current increases (from ‘www.bbc.co.uk’).

Exercise 34. Discuss the following questions.

1. What is an electric circuit?

2. What three connected parts constitute the circuit?

3. What is necessary for the circuit to work?

4. What basic types of circuits do you know?

5. How are the components arranged in a series circuit? parallel circuit?

6. As more and more resistors are added in parallel to a circuit, the equivalent resistance of the circuit ____________ (increases, decreases) and the total current of the circuit ____________ (increases, decreases).

7. What can you tell about the current and voltage of the components connected in series?

8. Two electric circuits are diagrammed below. For each circuit, indicate which two devices are connected in series and which two devices are connected in parallel (Fig.3).

Fig. 3. Electric Circuits

In series? ___________________ In series? ________________

In parallel? __________________ In parallel? _______________

Exercise 35. Complete the sentences with one or two words.

1. An electric current flows in a __________ circuit.

2. No electric current can flow in an __________ circuit.

3. We can turn an electric current on and off easily using a __________.

4. An electric current goes along only one path in a __________ circuit.

5. An electric current divides into branches in a __________ circuit.

6. A large electric current will flow if there is a __________ circuit.

Exercise 36. In series and parallel circuits, certain general rules may be stated with regard to quantities of voltage, current, resistance, and power. Express these rules, using your own words. For each of these rules, explain why it is true.

1. In a series circuit, voltage ___________________________________ .

2. In a series circuit, current ___________________________________. 3. In a series circuit, resistance _________________________________. 4. In a series circuit, power ____________________________________. 5. In a parallel circuit, voltage _________________________________ .

6. In a parallel circuit, current _________________________________ .

7. In a parallel circuit, resistance _______________________________ .

8. In a parallel circuit, power __________________________________ .

Exercise 37 Decide whether the following statements about an electric circuit are true or false.

1. Electrons are the mobile charge carriers in an electric circuit.	True / False
2. The path of charge flow from the + to the - terminal of the circuit can consist of nonconductive material.	True / False
3. Series circuits are characterized by the fact that there is a single pathway by which charge can travel from the + terminal to the - terminal.	True / False
4. During any single loop of charge around a series circuit, the charge will pass through each resistor in the circuit.	True / False
5. The overall resistance of a circuit increases as more and more resistors are placed in series in the circuit.	True / False
6. The total current in a circuit increases as more and more resistors are placed in series in the circuit.	True / False
7. Parallel circuits are characterized by the fact that there are multiple pathways by which charge can travel from the + terminal to the - terminal.	True / False
8. During any single loop of charge around a parallel circuit, the charge will pass through each resistor in the circuit.	True / False
9. The overall resistance of a circuit increases as more and more resistors are placed in parallel in the circuit.	True / False
10. The total current in a circuit increases as more and more resistors are placed in parallel in the circuit.	True / False
11. Suppose that three identical resistors with a resistance of 3-ohms are placed in series with a 12-Volt battery. The electric potential difference across each resistor is 12 Volts.	True / False
12. Suppose that three identical resistors with a resistance of 3-ohms are placed in parallel with a 12-Volt battery. The electric potential difference across each resistor is 12 Volts.	True / False
13. Suppose that three identical resistors with a resistance of 3-ohms are placed in parallel with a 12-Volt battery. The current in the circuit is 1 Amp.	True / False
13. Suppose that three identical resistors with a resistance of 3-ohms are placed in series with a 12-Volt battery. The current in the circuit is 4 Amps.	True / False

Exercise 38. You can see sentences describing some characteristics of series or parallel circuits. Write down them into the appropriate column (five characteristics in each column).

Series circuit	Parallel circuit

1. The current in all parts of the circuit is the same.

2. There is more than one path for current flow. Each current path is called a branch.

3. All of the branches connect to the same positive terminal and the same negative terminal. This means the same voltage is applied to all of the branches.

4. There is only one path for current to flow.

5. The sum of the branch currents equals the total current.

6. The same current flows through every component. You would get the same current measurement at any point along the circuit.

7. Open circuit in one component causes the entire circuit to be open.

8. Open circuit in one branch does not prevent current in other branches. 9. The total resistance is always less than the smallest resistance in any branch.

10. Individual resistances add up to the total resistance.

Exercise 39. Fill in the gaps in the text about circuits with the words from the box. Translate the text into Ukrainian.

switchboard sockets breaker circuits isolate switched conductor earthed short supply switch insulation neutral current

Lamps can be connected in a parallel circuit or in a series circuit. The supply has live and ________ conductors. On an alternating _______ (AC) supply, the difference between live and neutral is that conductors of the neutral side of appliances are ________ – that is, connected to earth.

Where an AC _______ enters a building, it is connected to a __________. This has a number of switches to allow different circuits in the building to be ________ on and off. Circuits include power circuits. These supply the ________ for the plugs on appliances. Usually, a circuit ________ is fitted to each circuit. This is safety ______ that switches off automatically if there is a problem. This may happen if a person touches a live conductor, or if there is a _______ circuit. A short circuit is when current flows directly from a live conductor to a neutral ________ – for example, due to damaged ________. Circuit breakers also allow _______ to be switched off manually, to _______ them (switch them off safely).

Speaking

Exercise 40. Test your knowledge of safe electrical circuits. Put a tick next to the people if they get electric shocks in these situations.

Exercise 41. Work in groups. Discuss the reasons why people get (don’t get) electric shocks in the situations in exercise 40. Explain your group’s reasons to the class.

Exercise 42. Read these captions. Write in the figure numbers in the diagrams they describe.

1. Fig.__. The person gets a shock because he touches the live wire in an earthed system.

2. Fig.__. The system is not earthed, but a tree touches the neutral wire and acts as an earth. The person touches the live wire. As a result, he gets a shock.

3. Fig.__. There are no trees in contact, and so this system is completely unearthed. Because two people touch a wire, they both get a shock.

4. Fig.__. The person touches the neutral wire in an earthed system, and as a result he doesn’t get a shock.

5. Fig.__. As this system is not earthed, the person can touch any wire without a shock.

6. Fig.__. In this non-earthed system, a tree touches the live wire and acts as an earth. Two people touch a wire. One touches the neutral wire, and therefore gets a shock. The other touches the live wire. Therefore he is safe.

Exercise 43. Explain the following terms in your own words.

Electric circuit Short circuit Live conductor Switch

Series circuit Parallel circuit Neutral conductor Switchboard

Language work. Cause and Effect.

Rule: As science is concerned with how and why things work, the grammar and description of cause and effect is very important. Cause and effect can be described in English in many ways. Cause: The system is earthed. Effect: You can touch the neutral wire without a shock. These words explain the cause of something: because, since, as. You can reverse the order of the clauses without changing the meaning. 1. You can touch the neutral wire without a shock, as / because/ since the system is earthed. 2. As / Because/ Since the system is earthed, you can touch the neutral wire without a shock. These words explain the result (or effect) of something: As a result, Therefore (at the beginning of a sentence), (and) so, (and) therefore, as a result (connecting to a previous clause). The system is earthed, and therefore / so / as a result you can touch the neutral wire without a shock.

Exercise 44. Connect two sentences using the word(s) in brackets. Make any necessary changes in punctuation and word order.

Example:

Ben touched an earthed live wire. He got a sock. (because, as a result)

1. Ben touched an earthed live wire because a result he got a sock.

2. Ben touched an earthed live wire, and as a result he got a sock.

1. Ron touched an earthed neutral wire. He was safe. (since, therefore)

2. Bill touched an unearthed wire. He didn’t get a shock. (as, and so)

3. Bob touched a live wire when a tree touched a neutral wire. He got a shock. (because, therefore)

4. Pete touched a live wire when a tree touched it. He was safe. (since, so)

5. Tom and Del touched an unearthed wire. They got a shock. (since, and therefore)

Grammar. Complex Subject.

Exercise 45. Translate the following sentences into English.

A) 1. Кажуть, що він знає 6 мов. Казали, що він знає 6 мов. 2.Кажуть, що він поїхав до Лондону. Казали, що він поїхав до Лондону. 3. Очікують, що угоду підпишуть цього тижня. 4. Повідомляють, що експедиція виїхала 15 травня. 5. Вважають, що він один з кращих пілотів нашої країни. 6. Кажуть, що цей будинок збудували 1000 років тому. 7. Відомо, що вона вивчила кілька іноземних мов. 8. Вважають, що ця фортеця була збудована у 12 столітті. 9. Повідомляють, що польська делегація прибула до Києва.

В) 1. Ця книга, здається, дуже цікава. 2. Він, здається, задоволений результатом своєї роботи. 3. Він, здається, знає цей предмет дуже добре. 4. Вона, здається, дуже багато читала з цього питання. 5. Здавалося, що вони не слухають його. 6. Сталося так, що ми зустрілися у Парижі. 7. Він виявився здібним фізиком. 8. Очевидно, ви забули про це.

С) 1. Погода, мабуть, зміниться. 2. Навряд чи він прийде. 3. Вони, очевидно, знають про це. 4. Цей фільм, безсумнівно, сподобається вам. 5. Він, очевидно, запізниться.

D) 1. Було чути, як наближався поїзд. 2. Кожного ранку її бачили у крамниці. 3. Чули, як вона співала у сусідній кімнаті. 4. Ніколи не бачили, як він сердився. 5. Було видно, як високо в небі пролетів літак.

Writing

Exercise 46. Translate the sentences into English using active vocabulary.

1. Послідовне і паралельне з'єднання в електротехніці – це два основних способи з'єднання елементів електричного кола. 2. Послідовним з'єднанням називається таке з'єднання, при якому кінець першого компонента кола сполучається з початком другого, кінець другого компонента сполучається з початком третього і т.д. 3. Сила струму в послідовному з’єднанні однакова на всіх ділянках, а напруга на кінцях усього з’єднання дорівнює сумі напруг на кінцях ділянках кола. 4. При паралельному з’єднанні провідників струм на ділянці кола дорівнює сумі струмів в окремих гілках цього кола, а напруги на кожній з гілок однакові. 5. Яка з електричних величин однакова для всіх провідників, з'єднаних паралельно? 6. Яку напругу використовують для побутових потреб? 7. Де використовується паралельне з’єднання? 8. Заземлення – навмисне електричне з'єднання будь-якої точки електричної мережі, електроустановки чи обладнання, із заземлюючим пристроєм. 9. Нульові (нейтральні) провідники позначаються літерою N і блакитним кольором. 10. Паралельне з'єднання провідників широко застосовують для під'єднання ламп електричного освітлення і побутових електроприладів до мережі. 11. Прикладом послідовного з'єднання провідників є з'єднання лампочок ялинкових гірлянд.

Exercise 47. Write a paragraph explaining from the point of view of physics why parallel connections are used in household wiring.