UNIT 19

 

I. Find out the words in the dictionary. Write them down and learn.

 

to remove, cluster, excess, to cancel, to rub, to constitute, sufficiently, to conduct, to contribute, insulator, to repel, to redistribute, to acquire, to undergo

 

II. Read the text. Use a dictionary, if necessary.

 

Text: “Electricity”.

 

Electricity and all its observable effects result from properties of stationary or moving elec­tric charges. There are two types, known as positive charges and negative charges, which exist in all substances and in all states of matter—solid, liquid, and gas.

All substances are made up of atoms, which consist of a nucleus (containing protons and neutrons) and orbiting electrons. Protons are positively charged, and electrons are neg­atively charged. Electrons can be removed from atoms and made to take part in various electrical phenomena. Protons, on the other hand, are usually found as part of a cluster of protons, neutrons, and electrons known as an ion. Ions may be positively or negatively charged, depending on whether they have an excess of protons or electrons.

In an ordinary piece of material the num­bers of protons and electrons within each atom, and therefore within the material as a whole, are equal. The positive and negative charges cancel each other to a large extent, and no electrical effects are observed. But if extra charges of one type are added, the mate­rial is left with a net charge and electrical ef­fects result.

Charges can be transferred from one mate­rial to another by rubbing them together. The study of these net stationary charges and their effects on each other constitutes the subject of static electricity or electrostatics.

In certain solid materials—metals in particular—some electrons are sufficiently "free" to be able to move through the material in a stream, forming an electric current. This is the basis of current electricity.

Solids, liquids, and gases can all conduct electric current if there are enough free elec­trons or ions. Electrons and positively charged ions move in opposite directions through the material, but in general both contribute to the current in a conducting medium. In an insula­tor, the electrons are too firmly fixed by chemical bonding to be able to move, and the mate­rial does not normally conduct electricity.

Static electricity. Static electricity can be produced by rubbing an insulating material such as a polyethylene rod with dry cloth. Charges are transferred so that the polyethylene is left with a net charge of one type and the cloth with a net charge of the other type. The rod and cloth then attract each other.

On the other hand, two rubbed rods of the same material repel, and the two cloths repel. Unlike charges thus experience a force of attraction, whereas like charges repel each other.

It is impossible to find a material that is repelled by both polyethylene and cloth.

Electrostatic induction. Although nothing is repelled by both polyethylene and cloth, uncharged pieces of material (for example, small scraps of paper) are attracted to both. This results from a phenomenon called electrostatic induction. The paper is neutral overall, but the influence of the charged polyethylene redistributes the charges in the paper. The polyethylene is positively charged and exerts an attractive force on the paper's negative charges The net result is mutual attraction.

Coulomb's law and electric field. The forces of electrostatic attraction and repulsion between charged objects are caused by the electric fields associated with them. The magnitude of the force between two charges depends on their size, distance apart, and the substance they are in.The force is proportional to the product of the charges, and inversely proportional to the square of the distance between them – a relationship known as Coulomb's law.

The force also decreases if the charges are placed in a material that undergoes electrical polarization, which separates the charges and has the effect of partly shielding them from each other. The amount of shielding is quantified by a property called the permittivity of a substance. A vacuum, which cannot undergo polarization, has the lowest permittivity, called the permittivity of free space. The permittivity of other materials depends on their structure; ionic substances such as water, for example, generally have higher permittivities than non-ionic substances.

 

III. Find the sentences that can’t be found in the text.

 

1. Modern physics defines the electromagnetic field as a distinct form of matter possessing definite properties.
2. The positive and negative charges cancel each other to a large extent, and no electrical effects are observed.
3. Electrons and positively charged ions move in opposite directions through the material, but in general both contribute to the current in a conducting medium.
4. The magnitude of the force between two charges depends on their size, distance apart, and the substance they are in.
5. In the case of a stationary charged body the magnetic fields, built up by the elementary charges constantly moving inside it cancel each other, and there is practically no magnetic field.

 

IV. Find English equivalents in the text.

 

1. полный (общий) заряд __________________________________
2. проводящая среда ______________________________________
3. электрический ток ______________________________________
4. свободный электрон ____________________________________
5. изолятор ______________________________________________
6. химическое соединение _________________________________
7. противоположные заряды ________________________________
8. одноименные заряды ____________________________________
9. влияние _______________________________________________
10. квадрат расстояния между _______________________________

 

V. Find Russian equivalents to the following expressions in the text.

 

1. permittivity ___________________________________________
2. as a whole ____________________________________________
3. to a large extent ________________________________________
4. in particular ___________________________________________
5. in general _____________________________________________
6. whereas ______________________________________________
7. to exert an attractive force ________________________________
8. inversely proportional ___________________________________
9. thus _________________________________________________
10. polyethylene rod _______________________________________

 

VI. Fill in the missing words.

 

1. There are two types, known as positive charges and negative charges, which exist in all _______ and in all _______ of matter _______ solid, liquid and gas.
2. Electrons can be removed from atoms and made to _______ _______ in various electrical phenomena.
3. The positive and negative charges _______ each other to a large extent, and no electrical effects are.
4. Solids, liquids and gases can all _______ electric current if there are enough _______ electrons or ions.
5. The polyethylene is positively charged and _______ an _______ force on the paper’s negative charges.
6. The forces of electrostatic _______ and _______ between objects are caused by the _______ fields associated with them.
7. The force is proportional to the _______ of the charges, and _______ proportional to the square of the distance between them.

 

VII. Fill in the prepositions, if necessary.

 

1. Electrons can be removed ___ atoms and made to take part ___ various electrical phenomena.
2. Protons, ___ the other hand, are usually found as part ___ a cluster ___ protons, neutrons, and electrons known as an ion.
3. Charges can be transferred ___ one material ___ another ___ rubbing them together.
4. The study ___ these net stationary charges and their effects ___ each other constitutes ___ the subject ___ static electricity or electrostatics.
5. It is impossible to find a material that is repelled ___ both polyethylene and cloth.
6. This results ___ a phenomenon called electrostatic induction.
7. The magnitude ___ the force between two charges depends ___ their size, distance apart, and the substance they are ___.

 

VIII. Define whether the sentences are true or false.

 

1. Electricity and all its observable effects result from properties of stationary electric charges.
2. Electrons can’t be removed from atoms.
3. Protons are usually found as part of a cluster of protons, neutrons, and electrons known as an ion.
4. Liquids and gases can’t conduct electric current even if there are enough free electrons.
5. Static electricity can be produced by rubbing an insulating material such as a polyethylene rod with a dry cloth.
6. It is easy to find a material that is repelled by both polyethylene and cloth.
7. A vacuum, which cannot undergo polarization, has the lowest permittivity, called the permittivity of free space.

 

IX. Practice with someone asking and answering.

 

1. What do electricity and all its observable effects result from?
2. How can charges be transferred from one material to another?
3. Can solids, liquids and gases conduct electric current?
4. How can static electricity be produced?
5. Is it possible to find a material that is repelled by both polyethylene and cloth?
6. What are the forces of electrostatic attraction and repulsion between charged objects caused by?
7. What does the magnitude of the force between two charges depend on?
8. What relationship is known as Coulomb’s law?
9. What is the permittivity of a substance?

 

X. Put questions to the following sentences.

 

1. There are two types, known as positive charges and negative charges. (Disjunctive)
2. Electrons can be removed from atoms and made to take part in various electrical phenomena. (General)
3. The positive and negative charges cancel each other to a large extent. (General)
4. This results from a phenomenon called electrostatic induction. (Special)
5. Unlike charges experience a force of attraction. (Alternative)
6. The forces of electrostatic attraction and repulsion between charged objects are caused by the electric fields associated with them. (What…?)

 

XI. Dictate the following sentences in English to your fellow-students. Check them together.

 

1. All substances are made up of atoms, which consist of a nucleus and orbiting electrons.
2. Electrons can be removed from atoms and made to take part in various electrical phenomena.
3. Charges can be transferred from one material to another by rubbing them together.
4. The forces of electrostatic attraction and repulsion between charged objects are caused by the electric fields associated with them.

 

XII. Dictation-translation.

 

1. Твёрдые тела, жидкости и газы могут проводить электрический ток, если имеется достаточное количество свободных электронов или ионов.

2. В изоляторе электроны слишком жестко фиксируются химическими соединениями, чтобы иметь возможность двигаться, и материал обычно не проводит электричество.

3. Противоположные заряды, таким образом, испытывают силу притяжения, в то время как одноименные заряды отталкиваются.

4. Сила пропорциональна произведению зарядов и обратно пропорциональна квадрату расстояния между ними – отношение, известное как закон Кулона.