Transcript 11 electricity and the mains

Electrical
symbols
Plug
problems
Earthing
Circuit
breakers
Electrical
safety
a.c.
theory
You should know all these by name
and what they do!
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Adding these in series will decrease the current
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It’s graph curves as it gets hotter
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This one is open
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You choose the one above the current
That should be flowing normally
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V
Connect in parallel to measure the pd
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Provides a pd
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Low resistance when connected the right way round
but no current will flow when it is the wrong way round
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Increasing light levels makes this
have a lower resistance
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Increasing the temperature makes this devices
resistance go down
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Changing its value increases and decreases the current
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A
Connected in series to measure the current
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More than 1 cell is called a ________
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This one is closed
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1 fixed resistor
2 lamp
3 open switch
4 fuse
5 voltmeter
6 cell
7 diode
8 LDR
9 thermistor
10 variable resistor
11 ammeter
12 battery
13 closed switch
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Plugs are a simple and safe way of connecting
things to a mains circuit. In Britain the squarepin fused plug is the most commonly used type.
When wiring a plug, check that:
• The wires are connected to the correct terminals:
Brown
to Live
Blue
to Neutral
Yellow and green to Earth
•There are no loose strands of wire
•The cable is held firmly by the grip
•A fuse of the correct value is fitted
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What is wrong with these plugs?
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E
L
N
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E
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N
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E
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N
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E
L
N
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E
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N
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E
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N
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E
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N
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E
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N
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E
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E
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When you plug
in an electrical
device, you are
connecting it
into a circuit.
The circuit
hasn’t got a
battery in it.
But the mains
Supplying
electricity which
Keeps changing
direction. We call this an alternating current
Insulated
cable
Live
fuse
230V a.c.
Neutral
Earth
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The ________
wire has a brown covering
The ________
wire is a safety wire
The ________
wire goes alternately + and –
The ________
wire has a blue covering
The ________
covering
wire has a green and yellow
Higher level
The live terminal of the mains supply
between a positive and negative voltage with
respect to the
terminal. The neutral
terminal stays at a voltage close to
with
respect to earth.
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answers
live
earth
live
neutral
earth
Higher level
Alternates
Neutral
zero
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The neutral wire is kept at zero potential. The live wire
potential alternates (changes) from positive to negative.
This causes an alternating potential difference (p.d.)
current
current
current
0 volts
p.d.
(volt)
previous
+338
-338
0 volts
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fuse
Earth
A fault, such as the live wire touching the metal
case can be dangerous. Earthing the case provides
a low resistance path so a large current flows to
earth, melts the fuse, breaks the circuit and
stops the current.
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Large
of current
Normalsurge
current
Push down to reset
after the fault has
been corrected
Iron
rocker
This coil of wire wrapped
round a piece of iron
is an electromagnet which
gets strong enough to
attract the rocker when
there is a surge of current
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