UNIT 21

 

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

 

property, to exhibit, to some extent, minute, diamagnetic, paramagnetic, ferromagnetic, solenoid, to cancel out, overall, to associate with, atomic dipoles, at random, inducing field, to align, susceptibility, to overwhelm

 

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

 

Text: “Magnetism”.

 

Magnetism is one of the fundamental properties of matter. All substances – even those such as glass, plastics, and wood, for example – exhibit magnetic properties to some extent, although most materials do so to such a minute degree that they are generally regarded as nonmagnetic. Only the metallic elements iron, nickel, and cobalt, and certain of their alloys (such as steel) are strongly magnetic; such substances are described as being ferromagnetic.

In general all materials can be classed as diamagnetic, paramagnetic, or ferromagnetic. Each behaves in a characteristic way when placed inside a current-carrying solenoid (that is, in a uniform magnetic field), depending on the electronic structure of the atoms and the arrangement of the atoms themselves within the material.

In a piece of diamagnetic material (such as bismuth or copper), the electrons in each atom are arranged so that their magnetic effects cancel out each other; hence a diamagnetic substance has no overall magnetic field associated with it. If a bar of the material is placed in an inducing field, however, the electron paths are slightly distorted. As a result, the substance becomes very weakly magnetized, but in the opposite direction to that of the inducing field. Hence the susceptibility (the ratio of the induced to the inducing magnetic field) of diamagnetic materials is very small and negative (typically about – 10^-5). If a bar of diamagnetic material is freely suspended in a strong uniform magnetic field, it aligns itself across the field.

In a paramagnetic material (such as platinum or aluminum) the magnetic effects of the electrons do not cancel completely and each atom acts like a minute, weak bar magnet. Under normal circumstances, these atomic dipoles are oriented at random and there is no overall magnetic effect. Under the influence of an inducing field, however, the dipoles tend to align with the field. As a result, the magnetic field induced in the substance is in the same direction as that of the inducing field, and a freely-suspended bar of paramagnetic material therefore aligns itself with the inducing field. But the dipole alignment is not complete and so the induced magnetism tends to be weak, although it is still strong enough to overwhelm the diamagnetic effect. The susceptibility of paramagnetic substances is small and positive (in the order of +10^-3).

Many substances are paramagnetic, but very few exhibit the third and most important form of magnetism – ferromagnetism. Ferromagnetic materials, such as iron and cobalt, display paramagnetic behavior, but much more strongly than most paramagnetic substances because many more atomic dipoles align when in an inducing field. Thus ferromagnetic materials have large, positive susceptibilities (often greater that +10³).

 

III. Find the words with negative meaning and translate them.

 

Extent, minute, nonmagnetic, ferromagnetic, uncertain, uniform, typically, useless, unlimited, uncompleted, dipole, paramagnetic, weakness, unimportant, display, susceptibility, unspecified, induce, regardless, decode, ratio, useless, atomic, disadvantage.

 

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

 

1. Magnetism is one of the fundamental properties of matter.
2. In fact, all magnetic effects are caused by movements of electric charges.
3. Only the metallic elements are strongly magnetic.
4. An important concept in magnetism is that of the magnetic pole.
5. A magnetic compass points to the earth’s magnetic north pole rather than the true, geographical North Pole.
6. A diamagnetic substance has no overall magnetic field associated with it.
7. The dipole alignment in a paramagnetic material is not complete and the induced magnetism in this case tends to be weak.
8. Magnetite, a form of iron ore, is the principal naturally-occurring ferromagnetic material.

 

V. Find English equivalents in the text.

 

1. проявлять магнитные свойства _____________________________
2. большинство материалов __________________________________
3. некоторые из их сплавов __________________________________
4. вести себя особым способом _______________________________
5. зависеть от электронной структуры атомов ___________________
6. внутри материала _________________________________________
7. расположены таким образом, что ____________________________
8. нейтрализуют друг друга ___________________________________
9. следовательно ____________________________________________
10. противоположное направление ______________________________
11. магнитная восприимчивость ________________________________
12. незначительный, слабый магнит _____________________________
13. под воздействием индуцируемого поля _______________________
14. то же самое направление ___________________________________
15. дипольная синхронизация __________________________________
16. проявлять поведение парамагнетиков ________________________

 

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

 

1. fundamental properties _______________________________________
2. to some extent ______________________________________________
3. such a minute degree __________________________________________
4. are generally regarded as _______________________________________
5. a uniform magnetic field _______________________________________
6. has no overall magnetic field ___________________________________
7. electron paths ________________________________________________
8. as a result ___________________________________________________
9. the ratio of the induced to the inducing magnetic field ________________
10. to cancel completely ___________________________________________
11. under normal circumstances _____________________________________
12. at random ____________________________________________________
13. to align with the field ___________________________________________
14. a freely-suspended bar __________________________________________
15. to overwhelm the diamagnetic effect ______________________________
16. many more atomic dipoles ______________________________________

 

VII. Fill in the missing words.

 

1. Magnetism is one of the fundamental _______ of matter.
2. All substances exhibit magnetic properties to some _______, although most materials do so to such a minute _______ that they are regarded as _______.
3. Materials can be classed as diamagnetic, _______, or ferromagnetic.
4. Each material behaves in a characteristic way when placed _______ a current-carrying _______.
5. In a piece of _______, the electrons in each atom are arranged so that their magnetic effects cancel out each other.
6. In a _______ material the magnetic effects of the electrons do not cancel completely and each atom acts like a minute, weak bar _______.
7. Materials which are _______ have large, positive susceptibilities (often greater than +10³).

 

VIII. Fill in the prepositions, if necessary.

 

1. All substances exhibit magnetic properties ____ some extent, although most ____ materials do so ____ such a minute degree that they are generally regarded ____ nonmagnetic.
2. Each material behaves ____ a characteristic way when placed inside a current-carrying solenoid, depending ____ the electronic structure ____ the atoms and the arrangement ____ the atoms themselves within the material.
3. In a piece of diamagnetic material such ____ bismuth or copper, the electrons ____ each atom are arranged so that their magnetic effects cancel ____ each ____ other.
4. If a bar ____ the diamagnetic material is placed ____ an inducing field, the electron paths are slightly distorted ____.
5. ____ normal circumstances, these atomic dipoles are oriented ____ random and there is no overall magnetic effect.
6. Under the influence ____ an inducing field the dipoles tend ____ align ____ the field.
7. Ferromagnetic materials display ____ paramagnetic behaviour, but much more strongly ____ most paramagnetic substances.

 

IX. Define whether the sentences are true or false.

 

1. Magnetism is the only fundamental property of matter.
2. Not all substances exhibit magnetic properties.
3. The metallic elements such as iron, cobalt, bismuth are regarded to be ferromagnetic.
4. In general all materials can be classed as paramagnetic or ferromagnetic.
5. Solenoid can be described as a uniform magnetic field.
6. The behavior of a definite material placed inside a current-carrying solenoid depends only on the electronic structure of the atoms within the material.
7. A diamagnetic substance has no overall magnetic field associated with it.
8. The ratio of the induced to the inducing magnetic field is called the susceptibility of a material.
9. Only diamagnetic materials possess negative susceptibilities.
10. The induced magnetism in a paramagnetic material tends to be very strong, much stronger than that in a ferromagnetic material.

 

X. Practice with someone asking and answering.

 

1. What is magnetism?
2. Do all substances exhibit magnetic properties?
3. What substances are generally regarded as nonmagnetic ones?
4. What types of magnetism can you name?
5. What influences the behavior of a material when placed inside a current-carrying solenoid?
6. What materials are called diamagnetic?
7. What kind of magnetism can we observe in a paramagnetic material under the influence of an inducing field?
8. What is the most important form of magnetism?
9. How do atomic dipoles in a ferromagnetic material act when in an inducing field?
10. Can you give the examples of diamagnetic and ferromagnetic materials?
11. What can be said about susceptibilities of different materials?

 

XI. Put questions to the following statements.

 

1. The electrons in each atom are arranged so that their magnetic effects cancel out each other.
2. Under the influence of an inducing field the dipoles tend to align with the field.
3. Ferromagnetic materials have large, positive susceptibilities. 

 

XII. Dictate the following statements in English to your fellow-students.

 

1. Magnetism is one of the fundamental properties of matter.
2. All substances exhibit magnetic properties to some extent.
3. In general all materials can be classed as diamagnetic, paramagnetic, or ferromagnetic.
4. Each behaves in a characteristic way when placed inside a current-carrying solenoid.
5. A diamagnetic substance has no overall magnetic field associated with it.
6. In a paramagnetic material the magnetic effects of the electrons do not cancel completely and each atom acts like a weak magnet.
7. Very few substances exhibit the most important form of magnetism – ferromagnetism.

 

XIII. Dictation-translation.

 

1. Магнетизм – одно из основополагающих свойств материй.
2. Все вещества в определенной степени проявляют магнитные свойства.
3. Лишь металлические элементы и некоторые из их сплавов являются сильными магнитами.
4. В целом, все материалы могут быть разделены на диамагнетики, парамагнетики и ферромагнетики.
5. В диамагнетике электроны в атоме расположены таким образом, что их магнитные свойства нейтрализуются друг за другом.
6. Вещество становится очень слабо намагниченным.
7. В парамагнетике магнитные свойства электронов полностью не исчезают, и каждый атом проявляет себя как слабый магнит.
8. В обычных условиях эти атомные диполи беспорядочно направлены.
9. Магнитная восприимчивость парамагнетиков мала и положительна.
10. Ферромагнетики проявляют парамагнитные свойства, но в гораздо более сильной степени, чем большинство парамагнетиков.