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LCA 1
Session 2
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Electric Current is produced when electrons
move through a material.
Metals have free electrons so that is why
electricity can travel through metals.
Materials that allow electricity to flow through
them are called “ Conductors”
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Current flows from + to –
Materials that Do Not allow current to flow
through them are called “Insulators”
Plastic, wood and rubber are insulators.
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A power source is needed to push the
electrons around the circuit.
This pressure is called electromotive force or
e.m.f. It is measured in Volts (V)
It is like a pump pushing water, the Voltage
pushes current.
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A Battery is made up of cells.
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Each cells gives 1.5V
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So if a Battery has 4 cells that means
4 X 1.5=6V Battery
The current from a Battery flows in one
direction and is called Direct Current (DC)
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In Ireland there is “Electric Ireland” (ESB),
“Bord Gais” and “Airtricity”
These companies supply Alternating Current
(AC).
The flow changes direction 50 times every
second. + to – then – to +.
They supply 220V
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Every circuit has to have voltage, current and
resistance.
Resistance is what tries to stop current flow.
Some conductors are made to have some
resistance and these are called resistors.
Name
Unit
Symbol
Ohm’s Law
Voltage
Volts
V
V
Current
Amps
A
I
Resistance
Ohm
Ω
R
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This is how voltage, current & resistance are
linked.
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Voltage
V=IxR
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Current
I = V/R
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Resistance
R = V/I
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Brown = Live
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Blue = Neutral
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Yellow/Green = Earth
Pg 186 Fig 14.14
Colour Codes
A 3-Pin Plug
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The function of the
Brown wire which is
called the Live is to
bring the current from
the power station to
the appliance that you
are using.
Live Wire is Brown
The function of the
Blue wire which is
called the Neutral is to
return the current to
the power station from
the appliance that you
are using.
Neutral Wire is Blue
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The Earth Wire
The metal body of electric appliances is
connected to the earth by means of earth
wire so that any leakage of electric current is
transferred to the ground. This prevents any
electric shock to the user. That is why
earthing of the electrical appliances is
necessary
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If for whatever reason
there is a fault, all the
metal parts of the
electrical appliance may
carry current which
means there is the
danger of electric shock.
The earth takes the
current to ground and
makes the appliance safe
Earth Rod
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How Circuit Breakers Work: Circuit Breaker: At
Work in Your Home
The circuit breaker is an absolutely essential
device in the modern world, and one of the most
important safety mechanisms in your home.
Whenever electrical wiring in a building has too
much current flowing through it, these simple
machines cut the power until somebody can fix
the problem.
Without circuit breakers (or the alternative,
fuses), household electricity would be impractical
because of the potential for fires and other
mayhem resulting from simple wiring problems
and equipment failures
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In a parallel circuit
each bulb gets a + and
a -. Therefore as seen
in the diagram the
power supply is a 9V
battery, this means
each bulb gets 9V and
if one blows the others
will light.
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It a series circuit each
bulb is wired after the
previous one. As the
diagrams show the
Voltage is 120V so
each bulb gets 60V.
If one bulb blows it will
break the circuit.
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Potential Divider
The potential divider forms the basis of many
electronic circuits and allows us to use a variety
of Sensors such as LDRs (light), thermistors
(heat) and moisture probes etc. The process can
be thought of as three distinctive parts or blocks.
Let us take as an example a situation whereby an
Alarm sounds if an LDR is placed in dark
conditions. The problem could be considered as
shown below.
The alarm is an LED
but it could be any
output device.
LED
LED
Note: we will look at how the transistor works later.
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With this device we can create a potential
difference
Because it has 3 legs and it’s resistance can
be changed manually.
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A Transistor is a an electronic switch
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It has 3 legs Collector, base & emitter
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Current will only flow through it if there is
0.7V at the base.
So it is turned on and off electronically.
0.4V
V is above 0.7 = Lights
V is below 0.7 = unlit
Resistor- Slows down the flow of current
Transistor- Is an electronic Switch
1 Resistor
2 Buzzer
Light Dependant Resistor- Resistance changes with changes in light.
1. LED
2. Transistor
3. Switch
4. Buzzer
C Switch
D Resistor
9V is the power of the battery, Voltage is the force it’s pushing the
current around the circuit with.
A=2
B= 1
A=LED –Indicator
B=Transistor-Switch
1.=Variable Resistor
2.=Resistor
3.=Transistor
4.=Bulb
Thermister – resistance changes
with changes in heat.