Iv. say whether these sentences are true or false:
1. when an extended conductor has the same potential at its ends, free
electrons are drifting from one end to another.
2. the wire and the electric source together form an electric circuit.
3. a path of any material will allow current to exist.
4. silver, copper and gold oppose very strongly.
5. the slighter the opposition is, the better the insulator is.
6. there is only one type of electric circuit.
7. we close the circuit when we switch on our electric device.
v. complete the sentences using the text:
1. the potential difference must be maintained by …
2. materials that offer slight opposition are called …
3. the best insulators are …
4. there are various kinds of electric circuits such as …
5. we “open” the circuit when …
6. we “close” the circuit when …
7. the “short” circuit is produced when …
8. a fuse is …
vi. answer the questions:
1. what concepts are very important in study of electric current?
2. what forms an electric circuit?
3. what materials are the best conductors and insulators?
4. what kinds of electric circuits do you know?
5. how can we open and close the circuit?
6. when are electrical devices connected in series?
7. what is an example of a series circuit?
8. what can you say about «parallel» circuits?
9. what does the short circuit often result from?
прилежащий текст к этим вопросам
electric circuits
the concepts of electric charge and potential are very important in the study
of electric currents. when an extended conductor has different potentials at its
ends, the free electrons of the conductor itself are caused to drift from one end to
the other. the potential difference must be maintained by some electric source
such as electrostatic generator or a battery or a direct current generator. the wire
and the electric source together form an electric circuit, the electrons are drifting
around it as long as the conducting path is maintained.
there are various kinds of electric circuits such as: open circuits, closed
circuits, series circuits, parallel circuits and short circuits.
to understand the difference between the following circuit connections is
not difficult at all. if the circuit is broken or «opened» anywhere, the current is
known to stop everywhere. the circuit is broken when an electric device is
switched off. the path along which the electrons travel must be complete oth-
erwise no electric power can be supplied from the source to the load. thus the
circuit is “closed” when an electric device is switched on.
when electrical devices are connected so that the current flows from one
device to another, they are said «to be connected in series». under such condi-
tions the current flow is the same in all parts of the circuit as there is only a
single path along which it may flow. the electrical bell circuit is considered to
be a typical example of a series circuit. the “parallel” circuit provides two or
more paths for the passage of current. the circuit is divided in such a way that
part of the current flows through one path and part through another. the lamps
in the houses are generally connected in parallel.
the “short” circuit is produced when the current can return to the source
of supply without control. the short circuits often result from cable fault or
wire fault. under certain conditions the short circuit may cause fire because the
current flows where it was not supposed to flow. if the current flow is too great
a fuse is used as a safety device to stop the current flow.
