9. Speak on the topic «eIectric Currents and Their Properties».

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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

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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

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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.

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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.