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

Ex. 4. Find synonyms in A and B.

Ex. 3. Find antonyms in A and B.

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

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

A. cell, device, current, lamp, wattage

B. power, battery, flow, bulb, appliance

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.

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

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

c. the flow of electricity through a wire

d. the unit for measuring electric current

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

f. 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?

Дата добавления: 2015-07-02