Учебные задания по английскому языку (90

READING

1. Read the text and mark the statements as TRUE or FALSE. Correct the FALSE ones.

a.In a series circuit the current flows to the negative terminal of the source.

b.The current does not change in a series circuit.

c.The resistances of each object in a series circuit form the total resistance.

d.The more objects are in a series circuit, the less voltage there is in the circuit.

e.In a parallel circuit the current in each branch and in the source is the same.

f.The total resistance of parallel objects is the sum of individual resistances.

g.A parallel circuit has only one path for the electric current.

h.The amount of current in a branch depends on the amount of its resistance.

Series Circuits

If various objects are arranged to form a single conducting path between the terminals of a source of electric current, the objects are said to be connected in series. The electron current first passes from the negative terminal of the source into the first object, then flows through the other objects one after another, and finally returns to the positive terminal of the source. The current is the same throughout the circuit. In the example of the light bulb, the wires, bulb, switch, and fuse are connected in series.

When objects are connected in series, the electric current flows through them against the resistance of the first object, then against the resistance of the next object, and so on. Therefore the total resistance to the current is equal to the sum of the individual resistances.

Voltage can be thought of as being used up by the objects in a circuit. The voltage that each object uses up is called the voltage drop across that object. Voltage drop can be calculated from the equation V = IR, where V is the voltage drop across

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Many circuits combine series and parallel arrangements. One branch ___ a parallel circuit, ___ example, may have ___ it several objects ___ a series. The resistances of these objects must be combined according ___ the rules ___ a series circuit. ___ the other hand, a series circuit may ___ one point divide ___ two or more branches and then rejoin. The branches are parallel and must be treated ___ the rules ___ parallel circuits.

3. Put each verb in brackets into a suitable verb form.

(1)___________(complicate) series-parallel circuits may (2)__________(analyze) by means of two rules called Kirchhoff’s laws. These rules make it possible

(3)_______(find) the amount of electric current (4)________(flow) through each part of any circuit, as well as the voltage across it. The first of Kirchhoff’s laws

(5)_______(state) that at any junction in a circuit through which a steady current

(6)________(flow), the sum of the currents flowing to the junction is equal to the sum of the currents flowing away from that point. The second law states that,

(7)_______(start) at any point in a circuit and following any (8)_______(close) path back to the starting point, the net sum of the voltage encountered (9)______(be equal) to the net sum of the products of the resistances encountered and the currents flowing through them. In other words, Ohm’s law (10)_______(apply) not only to a circuit as a whole, but also to any (11)_______(give) section of a circuit.

4. Write out the passage using one of the adjectives from the box.

SERIES SOURCES

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Sources of electric current can also be (1)________ in (2)_________ ways. Sources can be arranged in series by (3)__________ a terminal of one source to the

(4)________ terminal of the next source. For example, if the (5)_________ terminal of battery A is connected to the (6)_________ terminal of battery B, and the positive terminal of battery B to the negative terminal of battery C, then batteries A, B, and C are in series. The load is then placed between the positive terminal of battery C and the negative terminal of battery A.

When sources of electric current are connected in series, their (7)_______ voltage is

(8)___________ to the sum of their (9)___________ voltages.

5. Complete the text with words formed from the words in capitals.

in parallel unless they have (7)_______________the same voltage. APPROXIMATE

SPEAKING

Make a presentation on an arrangement of circuit for a particular purpose. WRITING

Think of a billboard advertising various fuses for particular electrical appliances.

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ASSESSMENT

Translate from English into Russian.

Electric circuits are classified in several ways. A direct-current circuit carries current that flows only in one direction. An alternating-current circuit carries current that pulsates back and forth many times each second, as in most household circuits. A series circuit comprises a path along which the whole current flows through each component. A parallel circuit comprises branches so that the current divides and only part of it flows through any branch. The voltage, or potential difference, across each branch of a parallel circuit is the same, but the currents may vary. In a home electrical circuit, for instance, the same voltage is applied across each light or appliance, but each of these loads draws a different amount of current, according to its power requirements. A number of similar batteries connected in parallel provide greater current than a single battery, but the voltage is the same as for a single battery.

The network of transistors, transformers, capacitors, connecting wires, and other electronic components within a single device such as a radio is also an electric circuit. Such complex circuits may be made up of one or more branches in combinations of series and series-parallel arrangements.

MODULE IV

UNIT ONE

ELECTRIC FIELDS

READING

1. Read the following text. Some phrases have been left out of the text. Choose from phrases A-I below to complete the gaps. There is one phrase you will not need.

A single electric charge can attract or repel, and it will demonstrate this ability as soon as another charge is brought near it. The ability to attract or repel can be thought

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of as being stored in the region around the charge. This region is called the electric field of force of the charge. All charged objects have electric fields (1)___________.

Lines of Force

An electric field can be visualized as consisting of imaginary lines called lines of force. Each line corresponds to the path that a positive charge would take if placed in the field on that line. The lines in the field around a positively charged object radiate in all directions away from the object, since the object repels positive charges. Conversely, the lines in the field around a negatively charged object are directed

(2)___________. If a positive and a negative object are placed near each other, their lines of force connect. If two objects with similar charges are placed near each other, the lines do not connect. Lines of force never (3)____________each other.

Lines of force are only imaginary. Nevertheless, the idea of lines of force helps in (4)____________an electric field.

Field Direction

When a charge is placed at any given point in an electric field, it is acted on by a force that tends to (5)___________it in a certain direction. This direction is called the direction of the field at that point. The field direction can be represented graphically by the lines of force near an electric charge.

Field Strength

The strength, or (6)____________, of a field at any point is defined as the force exerted on a charge of 1 coulomb placed at that point. For example, if a point charge of 1 coulomb is subjected to a force of 10 newtons, the electric field is 10 newtons per coulomb at that point. An object with a charge of 5 coulombs would be subjected to a force of 50 newtons at the same point.

Field strength is represented graphically by the closeness ((7)__________) of the lines of force. Where the lines are close together, the field is strong. Where they are (8)____________, the field is weak. Near a charge, the field is strong and the lines are close together. At greater distances from the charge, the field weakens and the lines are not as close together. The field strength values that the lines represent are relative, since a field can be drawn with as many lines as desired.

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Apush

Bdensity

Caround them

Dvisualizing

Etoward the object

Ffar apart

Gintegrity

Hcross

Iintensity

VOCABULARY PRACTICE

1.Explain the words and word combinations in bold in the text.

2.Replace the words underlined in each sentence with the most appropriate verb form from the box.

exert direct attract represent repel draw push weaken cross radiate

a.She asked him to move the table nearer to the wall.

b.This stove sends out sufficient heat.

c.The explosion made the building’s foundations less strong.

d.The new switch is an example of the latest innovations in technology.

e.We are pulled towards the earth by the gravitational force.

f.You’ll have to use all your eloquence to convince her.

g.Make a diagram and show the direction of the electric field.

h.This substance drives away mosquitoes.

i.He passed from one side of the street to the other side with resolute steps.

j.Our energies must be turned towards higher productivity.

3.Complete each sentence (a-g) with one of the endings (1-7).

a. A field is an area surrounding an object, in which a gravitational or

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electromagnetic force

b.The concept of fields was first introduced by English physicist Sir Isaac Newton

c.Gravitational and electromagnetic forces appear

d.Charged particles and massive bodies

e.Massive bodies exert a force

f.The fields exert an electromagnetic or gravitational force

g.The diagram shows that a positive test charge would be pushed

1.… to act at a distance.

2.… away from both charges.

3.… is exerted on other objects.

4.… are said to be the sources of electromagnetic and gravitational fields.

5.… to explain gravitational forces.

6.… on other objects.

7.… on each other.

4. Complete the text with words formed from the words in capitals.

5. Write out the passage using one of the words from the box.

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The most (1)_________mechanical phenomenon in electrical and magnetical experiments is the (2)__________action by which bodies in certain states set each other in motion while still at a (3)_________distance from each other. The first step, therefore, in (4)________these phenomena into (5)__________form, is to ascertain the (6)_________and direction of the force acting between the bodies, and when it is found that this force (7)________in a certain way upon the (8)__________ position of the bodies and on their electric or magnetic condition, it seems at first sight natural to explain the facts by (9)_________the (10)_________of something either at rest or in motion in each body, (11)__________its electric or magnetic state, and capable of acting at a distance according to mathematical laws.

UNIT TWO

ELECTRICITY AND MAGNETISM

READING

1. Read the text and complete statements 1-6 with the best ending A, B or C.

1) Opposite magnetic poles…

Apull towards each other.

Brepel each other.

Care neutral.

2)The strength of the poles…

Adoes not affect magnetic forces.

Binfluences magnetic forces.

Cis always the same.

3)Electromagnetism shows that electricity and magnetism…

Aare interdependent.

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Bstand in opposition.

Cexist separately.

4)Electric current…

Aexists around electric charges.

Bconsists of magnetic fields.

Cproduces magnetic fields.

5)The direction of the magnetic field…

Acannot be detected.

Bpresents circular movement around the conductor.

Ccoincides with the direction of the current.

6)The motor effect…

Ashows the relations between different magnetic fields.

Bindicates that magnetic fields are stronger than electric current.

Cis not applicable.

Many similarities exist between electric and magnetic phenomena. A magnet has two opposite poles, referred to as north and south. Opposite magnetic poles attract each other, and similar magnetic poles repel each other, exactly as happens with electric charges.

The force with which magnetic poles attract or repel each other depends on the strength of the poles and the distance between them. This relationship is similar to the

Coulomb’s inverse square law for electric charges.

The similarities between electric and magnetic phenomena indicate that electricity and magnetism are related. Electricity produces magnetic effects and magnetism produces electric effects. The relationship between electricity and magnetism is called electromagnetism.

Magnetic Effects of Electricity

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