ТОР 5 статей:
The Nature of Electricity
Practical electricity is produced by small atomic particles known as electrons. It is the movement of these particles which produces the effects of heat and light.
The pressure that forces these atomic particles to move, the effects they encounter opposition and how these forces are controlled are some of the principles of electricity.
Accepted atomic theory states that all matter is electrical in structure. Any object is largely composed of a combination of positive and negative particles of electricity. Electric current will pass through a wire, a body, or along a stream of water. It can be established in some substances more readily than in others, that all matter is composed of electric particles despite some basic differences in materials. The science of electricity then must begin with a study of the structure of matter.
Matter is defined as any substance which has mass (or weight) and occupies space. This definition should be broad enough to cover all physical objects in the universe. Wood, water, iron, and paper are some examples of matter. Energy is closely related to, but not to be confused with, matter. Energy does not have mass, and it does not occupy space. Heat and light are examples of energy.
The smallest particle of matter which can be recognized as an original substance was thought to be a unit called the atom. Recently scientists have found particles even smaller than atoms, but our theories are still based on the atom. The atom consists of a nucleus and a cloud of electrons. It is generally agreed that the electrons are small particles of electricity, which are negative in nature. These particles orbit the nucleus in much the same fashion that planets orbit a sun.
II. Guess the meaning of the following international words:
Electricity, electron, effect, structure, combination, material, mass, energy, atom, orbit.
III. Give the English equivalents for the words below:
1) производить; 2) частица; 3) тепло и свет; 4) напряжение; 5) сила; 6) вещество; 7) положительный; 8) отрицательный; 9) электрический ток; 10) вес; 11) ядро.
IV. Translate into Russian the words and expressions from the text:
1) atomic particle; 2) effects of heat and light; 3) encounter opposition; 4) principles of electricity; 5) composed (of); 6) pass through a wire; 7) structure of matter; 8) occupy space; 9) physical objects; 10) a cloud of electrons; 11) in the same fashion.
V. Complete the sentences using the text:
1. Electricity is produced by …
2. The effects of heat and light are produced by …
3. According to the accepted atomic theory all matter is …
4. Any object is composed of …
5. Matter is defined as …
6. Energy must not be confused with …
7. The atom consists of …
8. The smallest particle of matter is …
9. Most theories are based on …
10. Electrons are …
VI. Answer the questions:
1) What are the principles of electricity? 2) What must the science of electricity begin with? 3) Are there any differences between energy and matter? What are they? 4) What is recognized as an original substance now?
VII. Topics for discussion:
1) The nature of electricity;
2) The nature of matter;
3) Contents of atomic theory.
I. Read the text.
The electric current is a quantity of electrons flowing in a circuit per second of time. The unit of measure for current is ampere. If one coulomb passes a point in a circuit per second then the current strength is 1 ampere. The symbol for current isI.
The current which flows along wires consists of moving electrons. The electrons move along the circuit because the electromotive force drives them. The current is directly proportional to the e. m. f.
In addition to traveling through solids, however, the electric current can flow through liquids as well and even through gases. In both cases it produces some most important effects to meet industrial requirements.
Some liquids, such as melted metals for example, conduct current without any change to themselves. Others, called electrolytes, are found to change greatly when the current passes through them.
When the electrons flow in one direction only, the current is known to be d.c., that is, direct current. The simplest source of power for the direct current is a battery, for a battery pushes the electrons in the same direction all the time (i.e., from the negatively charged terminal to the positively charged terminal).
The letters a.c. stand for alternating current. The current under consideration flows first in one direction and then in the opposite one. The a.c. used for power and lighting purposes is assumed to go through 50 cycles in one second. One of the great advantages of a.c. is the ease with which power at low voltage can be changed into an almost similar amount of power at high voltage and vice versa. Hence, on the one hand alternating voltage is increased when it is necessary for long-distance transmission and, on the other hand, one can decrease it to meet industrial requirements as well as to operate various devices at home.
Although there are numerous cases when d.c. is required, at least 90 per cent of electrical energy to be generated at present is a.c. In fact, it finds wide application for lighting, heating, industrial, and some other purposes.
II. Guess the meaning of the following international words:
electric, ampere, symbol, proportional, industrial, metal, electrolyte, battery, generate.
III. Give the English equivalents for the words and word combinations below:
1) течь, протекать; 2) цепь, схема; 3) единица измерения; 4) провод; 5) электродвижущая сила; 6) твердое тело; 7) жидкость; 8) проводить (ток); 9) источник энергии; 10) постоянный ток; 11) переменный ток; 12) напряжение.
IV. Give Russian equivalents for the following:
1) to meet industrial requirements; 2) melted metals; 3) to push in the same direction; 4) negatively (positively) charged terminal; 5) power and lightning purposes; 6) long-distance transmission; 7) to operate devices; 8) to find wide application.
V. Say whether these sentences are true or false:
1. The symbol for current isI.
2. The electric current can flow only through liquids.
3. The current can be of two types: direct current and alternating current.
4. The alternating current flows in one direction.
5. A battery is the simplest source of power for the direct current.
6. Direct current finds wider application than alternating current.
7. Electrolytes don’t change greatly when current passes through them.
8. One of the great advantages of alternating current is the ease with which voltage can be changed.
VI. Fill in the blanks, using the words from the box:
A quantity of moving electrons flowing in a circuit is the a) _______. The current can flow through b) ________ and c) ________. Some liquids d) _______ current without any change to themselves. When the electrons flow in one direction only, the current is known to be e) _______. The current flowing first in one direction and then in the opposite one is f) _______. Such advantage of alternating current as alternating g) _______ finds wide industrial and household application.
VII. State the questions to the underlined words:
1. Melted metals conduct current without any change to themselves.
2. Alternating voltage can be changed to operate various devices at home.
3. A battery pushes the electrons in the same direction.
4. The alternating current is used for power and lightning purposes.
5. Alternating current accounts for 90 per cent of electrical energy generated now.
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