Basic Concepts
Lets have a look at a basic electrical circuit, in this case a BATTERY and a BULB. Each component
(battery and bulb) has its own unique symbol which we draw. To represent the wire that is used to join
components together, straight lines are used.
+
Bulb
Normally we do not write the names of
the components on the diagram, I have
done so in this case so that you can put
names to component symbols.
Battery
You already know from your work in Science that in this circuit the bulb will light up. But what makes the
bulb light?
CURRENT and VOLTAGE
Current is the rate of flow of CHARGE that is carried by negatively charged ELECTRONS (you can see
were the words ELECTRONICS and ELECTRICITY come from). The charge can be worked out using a
formula.
Q = I x t
In this formula Q stands for Charge (Measured in Coulombs)
I stands for Current (Measured in Amps)
t stands for Time (Measured in Seconds)
So CURRENT is a measure of how much charge is passed in a given time.
Now, VOLTAGE is the energy transferred for each unit of this CHARGE. Another way of looking at it is
that VOLTAGE pushes the CURRENT around the circuit.
For a circuit to work properly there must be a complete, unbroken, path for the current to flow from the
positive terminal of the battery to the negative terminal of the battery. This is shown below.
+
Circuit is complete, current will
flow and the bulb will light.
+
Circuit is broken, current will not
flow and the bulb will not light.
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Conductors and Insulators
For current to flow, the wire needs to be a CONDUCTOR. As you already know from your Science lessons
a conductor is a material which allows current to flow through it. Some materials conduct better than others
and examples of very good conductors are.
• Copper
• Silver
• Gold
The opposite of a conductor is a INSULATOR, which as you know is a material that does not allow current
to flow through it. Like conductors some insulate better than others, examples of very good insulators are.
• Rubber
• Ceramic
• Plastic
But did you know that there is a third type used in electronics? It’s a combination of a CONDUCTOR and
a INSULATOR and is called a SEMICONDUCTOR. The most common semiconductor material used in
electronics is Silicon.
You have probably heard of the word Silicon Chip before (or to give it its proper name a Integrated Circuit),
so what you were describing is a component that is a Semiconductor. There are a number of components
used in electronics that are semiconductors, but the most common are.
• Transistors
• Diodes
• Integrated Circuits
The picture above shows a wafer of Silicon (disc above left)
from which millions or billions of Integrated Circuits (IC’s)
will be made (above right).
The picture on the left shows people manufacturing these.
Notice how they are dressed like surgeons in a hospital. They
are working in a clean room, where there is no dust or foreign
bodies of any kind, even the air is thoroughly cleaned. This is
because even a particle of dust would cause real problems.
Nano-Technology
Just how small can we make things? Well, the picture on the left
shows a AMD Opteron Processor which has an area of just 114
square mm (10.7mm on each side if it were square).
Intel’s new SRAM (Static RAM) chips have 300 million transistors
in an area of 109 square mm (10.4mm on each side). Each SRAM
cell is 100 times smaller than a red blood cell.
Nano-Technology is currently at the cutting edge of electronics and
Actual size of Intel’s extends to the idea of creating nano-robots, smaller than a blood cell,
SRAM chip.
that can heal the body from inside.
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Voltage, Current and Resistance
Like all quantities, whether it be weight measured in grams or time measured in seconds, they all have units
(in these cases grams and seconds).
In electronics the units we use are as follows.
Voltage is measured in Volts (represented by the capital letter V)
Current is measured in Amps (represented by the capital letter A)
Resistance is measured in Ohms (represented by the Greek symbol Omega)
Now, we sometimes use Kg (or kilogram) for heavier weights or mSec (milliseconds) for shorter lengths
of time. It is the same with voltage, current and resistance. For example.
Mega (M)
Kilo (K)
is times 1,000,000
is times 1,000
so 1MV is 1,000,000 Volts
so 1KV is 1,000 Volts
Milli (m)
Micro (u)
Nano (n)
Pico (p)
is divide by 1,000
is divide by 1,000,000
is divide by 1,000,000,000
is divide by 1,000,000,000,00 0
so 1mV is 1/1,000 Volt
so 1uV is 1/1,000,000 Volt
so 1nV is 1/1,000,000,000 Volt
so 1pV is 1/1,000,000,000,000 Volt
Although this table shows the examples related to voltage, they same can be applied to current and resistance.
Measuring Voltage, Current and Resistance
To measure voltage, current and resistance we need to use a
tool called a MULTIMETER, an example of which is
shown in the picture on the left.
As the word multi means ‘many’ we can use this one tool to
measure many things, including voltage, current and
resistance.
To measure the red and black leads are placed in the correct
place in the circuit, and the dial turned to the correct scale.
The reading is then shown on the Liquid Crystal Display
(LCD). This makes it easy for us to read the value.
The probes must be placed correctly to measure voltage,
current and resistance, as shown in the diagrams below.
Measuring Voltage
Measuring Current
red probe (+)
+
Measuring Resistance
A
+
V
black probe (- or com)
R
You cannot measure
resistance with any
other
component
together with it in the
circuit.
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