Петербургский государственный университет путей сообщения императора Александра I

Кафедра «Иностранные языки»

Professional English

The English language course for senior students specializing in

Electrical Transport and Power Supply

Учебное пособие для студентов IV курса специальностей Электрический транспорт и Электроснабжение

2015

Unit 1

Basic Notions: Electric Current, Voltage and Resistance

Electric current is a flow of electrons, forming electric charge. Electric current is measured in amperes or amps (A). Electrons are particles with a negative charge, attached to atoms. When an electric current flows through a conductor, the electrons move from one atom to another. If the number of electrons flowing through a conductor increases then the amperage or ampage (current) increases.

The amount of current (in amps) flowing through a circuit partly depends on the electromotive force (EMF) of the electrical supply. EMF is measured in volts (V) and is called voltage.

The amount of current also depends on electrical resistance. It is a measure (in ohms - Ώ) of how easily current can flow through the conductors and components in a circuit.

Materials with high resistance are called electrical insulators. Materials that are good insulators are used to insulate conductors. An example is plastic insulation around electric wires.

The amount of current required by an electrical appliance or devices depends on the power of the appliance. The power is expressed in watts (W).

Ex. 1. Complete the word puzzle and find the key-word.

1.	ELECTRIC
2.	ELECTRIC
3.	ELECTRIC
4.	ELECTRIC
5.	ELECTRIC
6.	ELECTRIC
7.	ELECTRIC
8.	ELECTRIC

1. another term for amperage

2. provided by a battery, for example

3. measured as a wattage

4. allows current to flow through it

5. has very high electrical resistance

6. carried by moving electrons

7. another term for electrical “device”

8. the consequence of a person touching a live conductor

Ex. 2. Complete the extract about current and power calculations using the words in the box.

amps conductor current resistance voltage wattage

components circuit ohms supply volts watts

In electrical calculations, electromotive force is expressed by the letter E, resistance by the letter R, and current by the letter I (which comes from the word “intensity”).

According to Ohm’s Law: I = E/R.

In other words, the (1) … flowing through a (2)….. , measured in (3)….., equals the (4)..... of the electrical (5)….. , measured in (6)….. , divided by the total (7)….., measured in (8) … To work out the value of R, it is necessary to calculate the total resistance of all the (9)….. and connecting lengths of (10)….. that make up the circuit.

Once both the voltage and amperage are known, it is possible to work out the power, measured in (11)….., that will be consumed. Power (P) can be calculated using the equation P = EI. Therefore, (12)….. equals voltage multiplied by amperage.

Ex. 3. Find antonyms in A and B.

1. charge (v), positive, increase, static

2. dynamic, negative, discharge (v), decrease

Ex. 4. Find synonyms in A and B.

1. cell, device, current, lamp, wattage

2. power, battery, flow, bulb, appliance

Ex. 5. Read the text. Match the nouns in bold with the correct definitions.

A battery pushes electrons round a circuit. The flow of electrons is called a current. Current is measured in amperes (A).

Potential difference (PD), or voltage, is measured in volts (V). the greater the PD across a battery, the more potential energy each electron is given. The greater the PD across a bulb or other component, the more energy each electron loses as it passes through.

To make current flow through a conductor, there must be a potential difference (voltage) across it. Copper connecting wire is a good conductor and a current passes through it easily. However, a similar piece of nichrome wire is not so good and less current flows for the same PD.

The nichrome wire has more resistance than the copper.

1. a unit for measuring the force of an electric current

2. the opposition of a piece of electrical equipment to the flow of direct current

3. the flow of electricity through a wire

4. the unit for measuring electric current

5. a substance that allows electricity to pass along it or through it

6. the complete path of wires and equipment along which an electric current flows

Ex.6. How do you say it?

= is, equals, comes to. ½ = 0.5 One half equals point five.

׃ divided by, over. 10: 5 = 2 Ten divided by five is two.

· times, multiplied by. 10 · 5 = 50 Ten times five equals fifty.

+ and, plus, add. 10 + 5 = 15 Ten and five comes to fifteen.

- minus, less, subtract. 10 – 5 = 5 Ten less five is five.

Do the calculations by yourself and read them out:

1. 1,520: 20 = 4. 562 – 234 =

2. 150 · 30 = 5. 1,845 : 15 =

3. 325 + 720 = 6. 83 · 50 =

Ex. 7. The SI unit of resistance is the ohm (Ώ). The symbol Ώ is the Greek letter omega.

Resistance is calculated using the equation below:

Resistance (Ώ) = PD across conductor (V)

current through conductor (A)

We use these units for measuring higher resistances:

One kilohm equals one thousand ohms.

One megohm equals one million ohms.

a) Read out the calculations. Mind the SI units and symbols:

1. 2000 000 V/ 4 A = 0.5 M Ώ

2. 9600 V/20 A = 480 Ώ

3. 300 000 V/ 5 A = 60 kΏ

4. 120 V / 3 A = 40 Ώ

5. 150 000 V / 5 A = 30 k Ώ

6. 600 V / 6 A = 100 Ώ

7. 5 000 000 V/ 2.5 A = 2 M Ώ

8. 3500 V / 50 A = 70 Ώ

b) Work in pairs. Student A tells student B these calculations. Student B writes them down:

1. Twelve volts divided by four amps equals three ohms.

2. One thousand four hundred volts divided by forty amps equals thirty-five ohms.

3. Two hundred thousand volts divided by fifty amps equals four kilohms.

4. Five million volts divided by two amps equals two point five megohms.

Ex.8. Listen to the conversation between a teacher and a student and answer the questions:

1. What is the dialogue about?

2. What is the exam mostly about?

3. What concepts does the student confuse?

Ex.9. Listen again and complete the conversation.

Teacher: All right. We’ll start with terminology. List three types of electrical measurements.

Student: Okay. Three types are ……………………………………….

Teacher: Good. Now, ………..between an ohm and an amp?

Student: Hmm, well, an ohm …......in something, while an amp …………………………..

Teacher: That’s correct. So what’s ………. then?

Student: Voltage. Voltage …………………, right?

Teacher: Correct. Very good. Now, tell me how an insulator ……….. a conductor.

Student: Okay. A conductor……….. and an insulator ………….

Teacher: Good. So what property does an insulator exhibit?

Student: I know this, it’s ……………………. Oh! It’s ………………..

Teacher: Exactly. Insulators are ……….. Now, which type of current only flows …......?

Student: That’s AC.

Teacher: Actually, that’s ……..

Student: Oh, it’s ….. I always mix that up!

Ex.10. Make up similar dialogues speaking about some terms:

1. electric current;

2. electrical calculations;

3. potential difference;

4. resistance;

5. electromotive force.