Конспект урока по теме "Electric current"

ELECTRIC CURRENT

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 is I.

The current which flows along wires consists of moving electrons. The electrons move along the circuit because the e .m. f. 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:

a. 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:

b. 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 is I.

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:

direct current, solids, conduct, electric current, liquids, voltage, alternating current

             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.

VIII. Say some sentences about the types of electric current and its properties