²ʲв
:
³
ʳ
'
˳
˳
ϳ
'
㳿
Գ
Գ
Գ
Գ


Electric Currents and Their Properties

1. Remember the words and word combinations:

Conduction

Charge

Ion

Gaseous conductor

Liquid conductor

Mobile

A tiny crystal

Visible

A complex particle

Nucleus

At random

Driving force

To cause

To tend

Circuit

Electric current

To pass through

To measure

A direct current

An alternating current

 

A pulsating current

2. Read and translate the text:

Conduction is the name normally given to a movement or flow of charges. The charges are usually electrons, but may also be ions when the conduction takes place in gaseous or liquid conductors, in which the ions are mobile.

How does the current flow through a wire? A metal is made up of tiny crystals which are visible under a microscope. A crystal is a regular and orderly arrangement of atoms. As it was explained, an atom is a complex particle in which tiny electrons move around nucleus. When the atoms are tightly packed as they are in a metallic solid, some of the electrons move freely between the atoms. These are called free electrons. Ordinarily, the free electrons move at random through the metal. There must be some driving force to cause the electrons to move through the metal conductor. This driving force tending to produce the motion of electrons through a circuit is called an electromotive force or e.m.f. that moves electric charges from one point in the circuit to another.

When an electromotive force is applied to the ends of a wire the free electrons move in one direction. It is the movement of the free electrons in a conductor that includes an electric current. The greater the number of participating electrons, the greater is the flow of current.

No one has ever seen an electric current. We only know of the existence of a current by its effects. A

 

 

current can heat a conductor, it can have a chemical action when passing through a solution, or it can produce a magnetic effect. We can measure currents by observing their heating, their chemical, or their magnetic effects.

There are some kinds of current: a direct current (d.c.), an alternating current (a.c.), a pulsating current.

3. Answer the questions:

1. What is the conductor?

2. In what case may the charge be ions?

3. What is the metal made up of?

4. When do the electrons move?

5. What are the free electrons called?

6. How do the free electrons move?

7. When do the free electrons move in one direction?

8. When can current have a chemical action?

9. How can we measure current?

10. How many kinds of current do you know?

4. Correct the mistakes:

The charges are usually electrons.

A metal is made up of big crystals.

A crystal is irregular arrangement of atoms.

Once an atom was a complex particle.

The free electrons do not move at random through the

metal.

When an electromotive force is applied to the ends of

a wire the free electrons stay at their own places.

 

The greater the number of participating electrons, the

smaller is the flow of current.

A current cannot heat a conductor.

We can measure currents by observing their freezing.

There are only two kinds of current.

5. Make up a dialogue about the electric currents. Use the following expressions:

- Is made up of tiny crystals;

- A regular and orderly arrangement;

- Electromotive force;

- Electric current;

- To measure;

- Direct current;

- Alternating current;

- Pulsating current.

Imagine that you are an electrician and some of your friends ask you about electric currents, try to explain it them.

7. Read the dialogue and make up your own one:

Teacher: When will electrons move?

Student: If given a path, electrons dislodged from the

parent atom, will move.

T: Well, what do you know about the electric current?

S: The electric current is a quantity of electrons

flowing in a circuit per second of time.

T: And what is the unit of measure for current?

 

 

S: The unit of measure for current is the ampere. One

coulomb passing a point in a circuit per second, the

current strength is 1 ampere. The ampere is therefore a

rate unit.

T: Why do the electrons move along the circuit?

S: The electrons move around the circuit because the

e.m.f. drives them.

T: When is the rate of electron flow doubled?

S: It is doubled, if the force is doubled. It means that

other factors being constant, the current is directly

proportional to the e.m.f.

T: What other factor determining the magnitude of the

current do you know?

S: This is the ease with which the electrons are

allowed to pass along the circuit. This "ease" or

conductivity may be defined as the number of amperes

per volt in a circuit.

T: And when is a current proportional to the

conductivity?

S: All other factors being constant, the current is

directly proportional to the conductivity. If the

conductivity is doubled, the current will also doubled.

T: How is a magnetic field developed?

S: A stream of electrons in a circuit will develop a

magnetic field around the conductor along which the

electrons are moving.

T: What does the strength of the field depend upon?

S: The strength of the magnetic field depends upon the

current strength along the conductor.

T: And what about the direction of the field?

 

 

S: The direction of the field depends upon the direction of the current flow. T: When is the current called direct or alternating? S: If the force causing the electron flow is unidirectional, the current is called direct. The force changing its direction of effort periodically, the current is known as alternating. T: That will do!

8. Translate into English:

? , 1 . - . . ... , . ³, , . . .

Speak on the topic EIectric Currents and Their Properties.

 

Part 4

Capacity

1. Remember the words and word combinations:

Capacity

Insulated conductors

To be brought into contact

The charge spreads over

Potential

As soon as

The quantity of electricity

Depends upon its size

To be measured

To raise

Amount

To increase

To remain constant

Condenser

Artificially

2. Read and translate the text:

When two insulated conductors, one of which is charged, are brought into contact, the charge spreads over both conductors. The uncharged conductor becomes charged. A larger conductor receives a larger part of the charge. The potential of the two conductors becomes the same as soon as they are brought into contact, but the quantity of electricity is not the same

 

 

on each. The larger portion of the charge is on the larger conductor.

We say that the conductors have not the same capacity for electricity. The capacity of the conductor depends upon its size.

The capacity of the conductor is measured by the quantity of electricity which must be given to it in order to raise its potential to a given amount.

From this definition it is seen that if the capacity of a conductor increases while the quantity of electricity on it remains constant, its potential will become less.

Condenser. Any arrangement by which the capacity of a conductor is increased artificially is called a condenser.

3. Answer the questions;

1. When does the charge spread over both conductors?

2. What does the uncharged conductor become?

3. Does a larger conductor receive a larger part of the charge?

4. Have the conductors the same capacity for electricity?

5. How can we measure the capacity of the conductor?

6. When does the capacity of a conductor increase?

4. Read the following dialogue, act it out:

Teacher: What substance is a conductor of electricity? Student: Any substance or material which will afford continuous passage of an electric current when

 

 

subjected to a difference of electric potential is a

conductor of electricity.

T: When is a conductor said to be more efficient?

S: The greater the density of current for a given

potential difference the more efficient the conductor is

said to be.

T: What substances are efficient conductors and which

are poor ones?

S: Virtually all substances in solid or liquid state

possess the property of electric conductivity in some

degree. The metals, for example, are the best

conductors, many other substances, such as metal

oxides and salts, minerals and fibrous materials being

relatively poor conductors of electricity.

T: Which of less efficient conducting materials are of

great use in electricity?

S: Some of the less efficient conducting materials such

as carbon and certain metal alloys have very useful

applications in electrical arts, as well as the efficient

conductors such as copper and aluminum.

T: What substances are classed as non-conductors?

S: Certain substances are known to possess so little

conductivity that they are classed as non-conductors, a

better term being insulators or dielectrics.

T: Define a conductor, please.

S: A conductor is a body so constructed of conducting

material that it may be used as a carrier of electric

current. In ordinary engineering usage a conductor is a

material of relatively high conductivity.

T: Define a circuit, please.

 

S: An electric circuit is the path of an electric current or, more specifically, it is a conducting part or a system of parts through which an electric current is intended to flow.

5. Match the words with their definitions;

A conductor of electricity Non-conductors A conductor A circuit

Any substance or material which will afford continuous passage of an electric current when subjected to a difference of electric potential.

Certain substances that are known to possess little conductivity.

A body so constructed of conducting material that it may be used as a carrier of electric current.

A material of relatively high conductivity. A path of an electric current.

A conducting part or a system of parts through which an electric current is intended to flow.

 

 

6. Translate into English:

. . ֳ , , 䳺 ... . , . , .

, . , . .

© 2013 wikipage.com.ua - wikipage.com.ua |