Учебные задания по английскому языку (90

possible from A and flow to the other side of B. If that side of B is then connected to the ground by a good conductor, such as a metal wire, the electrons flow out through the wire into the ground. The ground can receive almost any amount of charge because Earth, being neutral, has an enormous capacitance. Object B is said to be grounded by the wire connecting it to Earth.

If this wire is then removed, B has a positive charge, since it has lost electrons to Earth. Thus B has been permanently charged by induction. Even if A is subsequently removed, B still remains positive because the wire has been disconnected and B cannot regain electrons from Earth to neutralize its positive charge.

VOCABULARY PRACTICE

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

2. Complete each sentence with an appropriate form of one of the verbs from the box.

a. This can prevent air from ________ freely to the lungs. b. You may be __________ if you do not pay the bill.

c. They had to _________ the money among schools in the area. d. This rod ________ the electrical equipment.

e. He did not ________ consciousness for several days. f. A magnet __________ steel.

g. By investing wisely she _____________ a fortune.

h. ________ magnetism is possible by holding a piece of iron near a magnet. i. This drug should __________ the poison.

j. The reptile’s prickly skin __________ nearly all of its predators.

3. Find English equivalents to the following words and word combinations.

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a. равномерно перераспределяться;

b. притягиваться к положительно заряженному предмету; c. отсоединить провод;

d. аналогично, подобным образом; e. отдавать электроны земле;

f. сообщать заряд;

g. быть заземлённым;

h.перетекать (об электронах).

4.Fill in the correct preposition.

A charged object will induce a charge __ a nearby conductor. __ this example, a negatively charged rod pushes some of the negatively charged electrons __ the far side __ a nearby copper sphere because like charges repel each other. The positive charges that remain __ the near side __ the sphere are attracted __ the rod. If the sphere is grounded so that the electrons can escape altogether, the charge __ the sphere will remain if the rod is removed.

5. Match each adjective (a-f) with one of the explanations (1-6). Use them in sentences of your own.

a.Negative_____________

b.Enormous____________

c.Near_________________

d.Positive______________

e.Neutral_______________

f.Possible______________

1.that can exist or happen;

2.of the sort of electricity produced by rubbing glass with silk;

3.very great, immense;

4.having no definite characteristics;

5.of that kind of electricity produced by rubbing wax, vulcanite, etc.

6.close to.

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SPEAKING

1. Speak on the role electricity plays in modern world.

WRITING

1. You are going to give a talk on static electricity. Make notes which may help you to explain the differences between charging by contact and charging by induction.

MODULE I ASSESSMENT

Translate from English into Russian in writing.

The ancient Greeks observed that amber, when rubbed, attracted small, light objects. About 600 BC Greek philosopher Thales of Miletus held that amber had a soul, since it could make other objects move. In a treatise written about three centuries later, another Greek philosopher, Theophrastus, stated that other substances also have this power.

For almost 2,000 years after Theophrastus, little progress was made in the study of electricity. In 1600 English physician William Gilbert published a book in which he noted that many substances besides amber could be charged by rubbing. He gave these substances the Latin name electrica, which is derived from the Greek word elektron (which means “amber”). The word electricity was first used by English writer and physician Sir Thomas Browne in 1646.

The fact that electricity can flow through a substance was discovered by 17th-century German physicist Otto von Guericke, who observed conduction in a linen thread. Von Guericke also described the first machine for producing an electric charge in 1672. The machine consisted of a sulfur sphere turned by a crank. When a hand was held against the sphere, a charge was induced on the sphere. Conduction was rediscovered independently by Englishman Stephen Gray during the early 1700s. Gray also noted that some substances are good conductors while others are insulators.

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MODULE II

UNIT ONE

ELECTRIC CURRENT

READING

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

1) According to the text a copper wire…

Adoes not let electric current flow through it.

Ballows charge to flow easily.

Cis a poor conductor.

2)Direct current…

Ais used in electric cells.

Bflows between two objects.

Cis of a much wider application than alternating current.

3)Alternating current…

Ais employed in a great number of electrical appliances.

Bis easy to understand.

Cflows in one direction.

4)Ohm’s law…

Aquantifies and compares electric currents.

Bshows what voltage and resistance are.

Cstates relations between current, voltage and resistance in circuits.

5)Materials that do not let electric current flow through them are called…

Aconductors.

Bdielectrics.

Ccapacitors.

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6) The charge can arc through an insulator from one object to another when the object has…

Aa positive charge.

Ba great charge.

Ca negative charge.

An electric current is a movement of charge. When two objects with different charges touch and redistribute their charges, an electric current flows from one object to the other until the charge is distributed according to the capacitances of the objects. If two objects are connected by a material that lets charge flow easily, such as a copper wire, then an electric current flows from one object to the other through the wire. Electric current can be demonstrated by connecting a small light bulb to an electric battery by two copper wires. When the connections are properly made, current flows through the wires and the bulb, causing the bulb to glow.

Current that flows in one direction only, such as the current in a battery-powered flashlight, is called direct current. Current that flows back and forth, reversing direction again and again, is called alternating current. Direct current is used in most battery-powered devices. Alternating current is used in most devices that are

“plugged in” to electrical outlets in buildings.

Other properties that are used to quantify and compare electric currents are the voltage (also called electromotive force) driving the current and the resistance of the conductor to the passage of the current. The amount of current, voltage, and resistance in any circuit are all related through an equation called Ohm’s law.

Electric current is measured in units called amperes (amp). If 1 coulomb of charge flows past each point of a wire every second, the wire is carrying a current of 1 amp. If 2 coulombs flow past each point in a second, the current is 2 amp.

Conductors and Insulators

Conductors are materials that allow an electric current to flow through them easily. Most metals are good conductors.

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Substances that do not allow electric current to flow through them are called insulators, nonconductors, or dielectrics. Rubber, glass, and air are common insulators. Electricians wear rubber gloves so that electric current will not pass from electrical equipment to their bodies. However, if an object contains a sufficient amount of charge, the charge can arc, or jump, through an insulator to another object. For example, if you shuffle across a wool rug and then hold your finger very close to, but not in contact with, a metal doorknob or radiator, current will arc through the air from your finger to the doorknob or radiator, even though air is an insulator. In the dark, the passage of the current through the air is visible as a tiny spark.

VOCABULARY PRACTICE

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

2.Replace the words underlined with the most appropriate adjective from the box.

a.The eclipse will be clearly seen in Western Europe.

b.I hope $10 is enough for the expenses of your journey.

c.He showed his movement in a straight line.

d.The two boys are not the same in their tastes.

e.Lightning is a usual phenomenon in many parts of the world.

f.Electrons are really small particles.

g.Most devices use current that repeatedly reverses its direction at regular intervals.

3. Fill in the correct preposition.

Battery, also electric cell, is a device that converts chemical energy ___ electricity. Strictly speaking, a battery consists ___ two or more cells connected ___ series or parallel, but the term is also used ___ single cells. All cells consist ___ a liquid, paste, or solid electrolyte and a positive electrode, and a negative electrode. The electrolyte is an ionic conductor; one ___ the electrodes will react, producing electrons, while

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the other will accept electrons. When the electrodes are connected ___ a device to be powered, called a load, an electrical current flows.

Batteries ___ which the chemicals cannot be reconstituted ___ their original form once the energy has been converted (that is, batteries that have been discharged) are called primary cells or voltaic cells. Batteries ___ which the chemicals can be reconstituted ___ passing an electric current ___ them ___ the direction opposite that

___ normal cell operation are called secondary cells, rechargeable cells, storage cells, or accumulators.

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

friction provide the resistance to the flow of a fluid in a pipe, and (9)____INSULATE

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

ELECTRIC INSULATION

The perfect insulator for electrical applications (1)_____(be) a material that is absolutely nonconducting; such a material (2)____(not exist). The materials

(3)______(use) as insulators, although they do conduct some electricity, have a resistance to the flow of electric current greater than that of good electrical conductors such as silver and copper. Materials that are good conductors

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(4)_____(have) a large number of free electrons (electrons not tightly bound to atoms) available (5)______(carry) the current; good insulators have few such electrons.

In ordinary electric (6)________(wire), plastics are commonly used as insulating

(7)________(sheathe) for the wire itself. Very fine wire, such as that used for

(8)_______(wind) coils and transformers, may (9)_________(insulate) with a thin coat of enamel. The internal insulation of electric equipment may (10)______(make) of mica or glass fibers with a plastic binder. Electronic equipment and transformers may also (12)_____(use) a special electrical grade of paper. High-voltage power lines are insulated with units (13)_______(make) of porcelain or other ceramic, or of glass.

UNIT TWO

VOLTAGE AND RESISTANCE

READING

1.Scan the first paragraph of the article and say what the voltage is and what its amount depends on.

2.Skim the second paragraph and state the reason for the electric current flow to be impeded.

3.Read the rest of the text and answer the questions.

a.What is the optimal resistance for conductors? for insulators?

b.How is resistance related to the characteristics of a conductor?

c.What is superconductivity?

Voltage

When the two terminals of a battery are connected by a conductor, an electric current flows through the conductor. One terminal continuously sends electrons into the conductor, while the other continuously receives electrons from it. The current flow is caused by the voltage, or potential difference, between the terminals. The more willing the terminals are to give up and receive electrons, the higher the voltage.

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Voltage is measured in units called volts. Another name for a voltage produced by a source of electric current is electromotive force.

Resistance

A conductor allows an electric current to flow through it, but it does not permit the current to flow with perfect freedom. Collisions between the electrons and the atoms of the conductor interfere with the flow of electrons. This phenomenon is known as resistance. Resistance is measured in units called ohms.

A good conductor is one that has low resistance. A good insulator has a very high resistance. At commonly encountered temperatures, silver is the best conductor and copper is the second best. Electric wires are usually made of copper, which is less expensive than silver.

The resistance of a piece of wire depends on its length, and its cross-sectional area, or thickness. The longer the wire is, the greater its resistance. If one wire is twice as long as a wire of identical diameter and material, the longer wire offers twice as much resistance as the shorter one. A thicker wire, however, has less resistance, because a thick wire offers more room for an electric current to pass through than a thin wire does. A wire whose cross-sectional area is twice that of another wire of equal length and similar material has only half the resistance of the thinner wire. Scientists describe this relationship between resistance, length, and area by saying that resistance is proportional to length and inversely proportional to cross-sectional area.

VOCABULARY PRACTICE

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

2.Find English equivalents to the following word combinations. a. при обычной температуре

b. разность потенциалов

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c. одинакового диаметра d. электродвижущая сила

e. площадь поперечного сечения f. пропорционально длине

g. обеспечивать больше пространства

h.падать до нуля

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

THE DISCOVERY OF SUPERCONDUCTIVITY

Dutch physicist Heike Kamerlingh Onnes sometimes (1)________(call) the

“gentleman of absolute zero” for his (2)_________(pioneer) work in cryogenics, the study of materials at extremely low temperatures. Onnes (3)______(begin) his lowtemperature work because of his interest in the behavior of gases. He went on

(4)______(become) the first person (5)_______(liquefy) helium and the first

(6)_______(discover) that some metals, when sufficiently (7)______(cool),

(8)______(become) superconductors—that is, materials that have no resistance to the flow of an electrical current.

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

a.The relationship between current, voltage and resistance…

b.Under normal conditions, resistance…

c.A conductor’s resistance…

d.Energy is required…

e.The rate at which energy is supplied…

f.Superconducting magnets…

g.The discovery of better superconducting compounds…

1…is constant in conductors made of metal. 2…to a device is called power.

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