Download What is Electronics?

La Salle College
Design & Technology
Electronics
What is Electronics?
Simply speaking, electronics is the study of how to control electric current using electronic
components. It is applied in many electronic products, for example Hi-Fi, computers, telephones
and television sets.
Terms of Electronics
 Current (I)
The movement of electric charges is called current.
Unit: Ampere (A)
 Voltage (V)/Potential Difference
The potential difference, which is also called voltage, is the invisible force that makes electric
charges move. Electric charges flow from high potential to low potential. The greater the potential
difference is, the faster the charges move.
Unit: Volt (V)
 Resistance (R)
It is the opposition to current. A conductor conducts electricity while an insulator does not. A
conductor will conduct electricity “better” if its resistance is low.
Unit: Ohm (  )

Ohm's Law
Current = Potential Difference / Resistance
The Ohm’s Law describes the relationship among current, resistance and potential difference in a
circuit. To have a large current, the potential difference must be increased or the resistance must be
decreased.
 Direct Current (D.C.)
It is a current which can only move in one direction in a circuit. The current produced by dry cells
is the direct current and its voltage is usually low.
 Alternating Current (A.C.)
It is a current which moves forward and backward alternately in a circuit. The domestic power
supply gives an alternating current. The voltage is usually high and dangerous.
 Circuit
It is a closed path which allows movement of electric charges. Electricity will only flow if the
circuit is “closed”.
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Circuit Diagram
It is a special drawing that uses symbols and conversions to present a
circuit (Fig. 1). In circuit diagrams, conductors (usually wires) are
represented by straight lines drawn parallel or at 90 to each other.
Fig. 1
Series and Parallel
There are two kinds of electrical circuit - series and parallel. In a
series circuit, the electrons have no choice on the path that they can
move, i.e. there are no branches in the circuit (Fig. 1). In a parallel
circuit, the electrons do have choices on the paths that they can
move (Fig. 2).
Fig. 2
Electronic Components
 Fixed-valued Resistor
The resistors are used to control the current in a circuit. For a fixed-value resistor, the value of its
resistance cannot be changed. It appears in most circuits.
Symbol
Appearance
Resistor color coding
Resistors are often so small that it would be difficult to show the value of the resistance on them.
To overcome this problem, fixed-value resistors are usually marked with four colored bands. From
the first three bands, the value of resistance can be worked out. The 4th band tells us the tolerance
of the resistance.
E.g. “Black-Red-Blue-Gold” means that the resistance is 2 000 000   5% (2M 5%).
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Gold
Silver
(None)
1st band
2nd band
3rd band
4th band
0
1
2
3
4
5
6
7
8
9
-
0
1
2
3
4
5
6
7
8
9
-

0
00 
000 
0 000 
00 000 
000 000 
-
 1%
 2%
 5%
 10%
 20%
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 Capacitor
It is used to store (charge) electrical charges. It releases (discharges) the electrical charges stored
when necessary. We usually measure the capacitance in F, which stands for microfarad (one
millionth of a farad).
Symbol
Appearance
+
 Integrated Circuit (I.C.)
As mentioned before, circuits are built by using numerous components such as resistors, capacitors,
etc. It may be bulky for complicated circuits. Since 1960s, single components called Integrated
Circuits have been manufactured to replace large numbers of components. At the beginning, an
integrated circuit probably contained the equivalent of about 50 components. But nowadays, it is
possible to manufacture integrated circuits that contain the equivalent of about 1 000 000
components.
Symbol
4
Appearance
8
7
3
LM
555
2
6
5
1
 Switch
It turns the current in a circuit on or off, that means, makes it close or open respectively.
Symbol
Appearance
 Loudspeaker
It converts electrical signals into sound.
Symbol
Appearance
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 Dry cell/Battery
It provides electrical energy to the circuit. The current generated by dry cells is direct current. A
group of dry cells connected together in the same direction is called a battery.
Symbol
Appearance
battery
dry cell
 Wires
It is used as conductor of electricity in a circuit, to connect components together.
Symbol
Appearance
If lines cross and the conductor are not connected, the lines are simply shown as crossing over each
other. If lines cross and conductors are connected, a dot is shown. (Fig. 3)
Wires cross but not connected
Wires connected
Fig. 3
For further information, you can refer to your Integrated Science textbook:
Interactive Science (2004), written by HW Ip, WL Lam &, TP Wong, Longman Hong Kong
Education. Relevant information is printed on P.83 – 113 of Book 2A
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Soft Soldering
Soft soldering is a basic joining method for electronics work (Fig. 4). It
makes a permanent joint between two pieces of metal. A soft soldering
joint is made by melting the alloy of tin and lead, which is called solder
(Fig. 5), and making it 'flows' over the two joining parts. The joining parts
are heated to a temperature just a little higher than the melting point of the
solder. The flux (Fig. 6), which is used to keep the work pieces clean
during soldering and make the solder flow easily, is also applied to the
joining parts. Usually, electric soldering bit (Fig. 7) is used for heating the
joining parts.
Solder and flux
There are several types of solder for soft soldering. For electronics work, a
tin-lead alloy (60/40) is usually used. The melting point of this alloy is low
(about 200 - 300C). For most solders, the flux is contained in cores
throughout the length of the solder. Thus the correct amount of flux is
always applied to the joint with the solder.
Procedure of soft soldering
1. Apply flux to the joining parts. (This step can be exempted if you are
using solder containing flux in core)
2. Using the electric soldering bit, heat the copper foil on the printed
circuit board (Fig. 8).
3. Then also heat the metallic “legs” of the electronic component.
4. Apply solder to the joint (Fig. 4).
5. The solder will flow evenly around the joint if both the copper foil and
“legs” are hot enough.
6. Remove the electric soldering bit.
7. Cut the excessive part of the metallic “legs”.
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Precautions
In soft soldering, great care must be taken not to overheat the joining parts
otherwise damage to the electronic components will occur. The copper foil
on the printed circuit board may melt away or damages may be caused to
heat-sensitive components like transistors, capacitors, etc.
Handle the electric soldering bit with great care. In case of heat burn,
report to your teacher at once and cool the wound with flashing water.
Fig. 8
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