Basic HTML Version
20
SECTION 1
The electric circuit
A
CLOSED CIRCUIT
Inelectrical applications
requiring the use of
current, the components
are arranged in the form
of a circuit. A circuit can be defined as a
path
f
or
current to flow along. Any electric circuit has three
important characteristics:
1. there must be a source of potential difference,
without the applied voltage, current cannot flow;
2. there must be a complete path for current flow, from
one side of the applied
voltage source
,
through
the external circuit, and returning to the other side
of the voltage source;
3. the current path normally has resistance. The
resistance is in the circuit for the purpose of either
generating heat or limiting the amount of current.
To sum up: a closed circuit, or simply a circuit, is a
closed path that has V to produce I with R to limit the
amount of current.
V stands for:
.......................................................................................
I stands for
:
.......................................................................................
R stands for:
.......................................................................................
The circuit offers a way of using the energy of a
battery as a source of voltage.
A battery will have a potential difference V with or
without the circuit.
However, a battery alone does not do any work when
producing load current.
B
OPEN CIRCUIT
When a part of the
path is open or
broken, the circuit
is said to be open
because there is no continuity in the conducting path.
Examples of open circuits are found in
connecting
wires
. The resistance of an open circuit is infinitely
high. There is no current in an open circuit
C
SHORT CIRCUIT
There is a
short
circuit
when the
voltage source has a
closed path across its
terminals, but resistance is practically zero. The result
is too much current. Usually a short circuit is a bypass
across the load resistance. For instance, a “short”
across the conducting wires for a
bulb
, produces too
much current in the wires and no current through the
bulb. Then the bulb is said to have shorted (out). The
bulb is not damaged, but the wires can become hot
enough to burn unless the line has a
fuse
: a device
which breaks the circuit, shutting off the current if it
goes too high and could start
overheating
wires
which could then cause a fire.
Types of Circuits
8
Brainstorming
Read the first part of the passage below and fill in the blanks. Then go on reading and
note when you find the words
electric
and
electrical
. After reading answer the following questions.
a
Did you find the two words in the same situations?
b
Do you think that they are synonyms?
c
Guess the classes of the two words.
d
Try to explain what they mean and how or when they are used.
TEXT 3
9
Find the right answer to each question.
1
Which elements must there be in an electric circuit?
a
When there is too much current.
2
When is a circuit open?
b
When there is no continuity in the
conducting path.
3
When is there a short circuit?
c
They are: a potential difference, a
path, a resistance.
bulb
lampadina
connecting wires
fili di collegamento
fuse
fusibile
(to) overheat
surriscaldare
path
passaggio, tracciato
short circuit
corto circuito
voltage source
fonte di energia
TECHNICAL ENGLISH
BATTERY
SWITCH 1
LAMP
SWITCH 2
BATTERY
SWITCH 1
SWITCH 2
BATTERY
SWITCH 1
L
SWITCH 2
Progetto FOR ELECTRONICS_unit_1.indd 20
10/01/