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Basic
Electronics
A. Circuit
fundamentals
A circuit is a closed path for electron
(current) flow
A circuit must have four
key elements
-
A voltage source
-
A load
-
A complete path
-
A switch
Voltage
is the force in a voltage source and is measured in VOLTS.
The symbol for voltage is €œV€.
An example of a voltage source
is a battery
Current
is (how fast) the measure of the flow of electricity in a circuit and it is
measured in Amps.
€œAmps€ is a short form for Amperes.
The symbol for Current is €œI€.
Loads can be generally defined as the
resistance to the flow of current in a circuit.
Resistance is the opposition to
current flow. The symbol for
resistance is €œR€.
A resistor is a small electronic component used to add
resistance (or load) in a circuit.
Resistor values are given in ohms (Ω - this is the symbol for Greek letter
"omega").
B. The Resistor colour
code
-
The code is a convenient way to tell the
resistance of a resistor.
-
(It is also used for other components such
as capacitors)
-
Coloured bands are placed on a resistor.
Each band has a numerical value.
-
Bands are read from left to right.
1 - First colour band = 1st digit
2 -
Second colour Band = 2nd digit
3 - Third colour Band
= Multiplier
The last band (usually separated from
the others) = the tolerance (how accurate the R value is)
Resistors colour codes - The following table
should be memorized
|
COLOUR OF BAND
|
FIRST BAND
|
SECOND BAND
|
Multiplier
|
Tolerance
|
|
BLACK
|
0
|
0
|
1
|
|
|
BROWN
|
1
|
1
|
10
|
|
|
RED
|
2
|
2
|
100
|
|
|
ORANGE
|
3
|
3
|
1,000
|
|
|
YELLOW
|
4
|
4
|
10,000
|
|
|
GREEN
|
5
|
5
|
100,000
|
|
|
BLUE
|
6
|
6
|
1,000,000
|
|
|
VIOLET
|
7
|
7
|
10,000,000
|
|
|
GRAY
|
8
|
8
|
100,000,000
|
|
|
WHITE
|
9
|
9
|
1,000,000,000
|
|
|
SILVER
|
|
|
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+ or - 10%
|
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GOLD
|
|
|
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+ or - 5%
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EXAMPLE: What is the value of resistance of a
resistor with the following coloured bands:
Yellow, green, red, gold
Solution
Yellow
= 4
\ the
first number = 4
Green = 5
\ the second number = 5
Red (in the third band) = X100
THE VALUE OF THE RESISTOR IS 45x100 = 4,500
ohms OR 4.5kΩ(4.5 KILO-OHMS)
Since the last band is gold, the accuracy of
this resistor is
± 5%.
This means that the resistor can have a
resistance value that could go from a high of
4725
Ω
to a low of
4275
Ω.
C.
Type of Circuits
There are
basically two types of circuits:
-
Series Circuits
-
Parallel Circuits
Series Circuits
In
series circuits there is one path for current flow.
This is an example of
series circuit
Parallel circuits
In parallel circuits there could be two or more paths for current flow
This is an example of a parallel circuit
We use standard symbols to
draw electronic circuits or schematics.
Here are some of the standard symbols
used.
|
Component |
Symbol |
|
Light Bulb |
 |
|
Resistor |
 |
|
Battery |
 |
|
Diode |
 |
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LED |
 |
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Switch |
 
|
|
Wire |
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REVIEW EXERCISES
A.
Find the
resistance for the following resistors and state the high/low range for each.
1. brown, black, red, gold
2. orange, yellow, red, silver
3. blue, black, green, silver
B.
Draw a
circuit diagram, using proper symbols to show the following
1.
A
series circuit with a battery, an ammeter, and a light bulb
2.
A
parallel circuit with a battery, a voltmeter, an a light bulb
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