ELECTRICAL APPLIANCES

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ELECTRICAL APPLIANCES
Our home is full of electrical appliances. They
change electricity into a more useful form of
energy.
Some appliances use more energy than others
their POWER RATING is higher.
Plugs are fitted with a fuse to protect the flex
connected to the appliance. As a general rule a
3A fuse is fitted for appliances that use up to
700W and a 13A fuse is fitted for appliances that
use more than 700W.
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The table contains some general information
Appliance Energy change Flex 2/3 core Power rating (W) Fuse (A)
Clock 2 10 3
Table lamp 2 100 3
T.V. 3 250 13
Hairdrier 3 1000 13
Iron 3 1200 13
Kettle 3 2000 13
Fire 3 3000 13
Cooker 3 11500 13
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FUSES
Fuses are used to limit the current flowing
through a circuit or into an appliance. A fuse
will melt when the current flowing through it
exceeds the rating of the fuse. This protects the
flex from overheating which could result in a
fire. The circuit is then broken and the flow of
current stops.
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HUMAN CONDUCTIVITY
The human body is a conductor of electricity.
Water (moisture) increases the bodys ability to
conduct.
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EARTH WIRE
The earth wire is a safety feature which prevents
the metal casing of an appliance becoming
dangerous to touch when a fault occurs. A large
current will flow through the earth wire and the
fuse will melt, protecting the appliance.
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CIRCUIT BREAKER
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.
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DOUBLE INSULATION
Double insulated appliances If you are fitting a
plug to a double insulated appliance (labelled
with the double insulated symbol), you should not
have an earth conductor in your flex.
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3 PIN PLUG

• Know colours and names of each wire.

• Note how outer insulation is secured by cable
  grip.

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ELECTRIC CHARGE
A current of electricity is a steady flow of
electrons. When electrons move from one place to
another, round a circuit, they carry electrical
energy from place to place like marching ants
carrying leaves. Instead of carrying leaves,
electrons carry a tiny amount of electric charge.
Charge is calculated using
Q
Q It
t
I
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MEASURING CURRENT 1
LEARNING To build a series circuit and measure
the INTENTION current at different points in
the circuit.
APPARATUS power supply, 2 lamps, connecting
leads, switch and ammeter
.
.
C
.
A
B
METHOD Build circuit and measure current at
points A, B and C
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RESULTS
POSITION CURRENT (A)
A
B
C
CONCLUSION
Current is the same at all points in a series
circuit.
IA IB IC
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MEASURING VOLTAGE
L. INT To build a series circuit and measure
the voltage across L1, L2 and Vs.
APPARATUS power supply, 2 lamps, connecting
leads, switch and voltmeter
Vs

-
L1
L2
METHOD Build circuit and measure voltage
across L1, L2 and Vs.
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RESULTS
POSITION VOLTAGE (V)
L1
L2
Vs
CONCLUSION
The supply voltage equals the sum of the voltages
across the 2 lamps
Vs V1 V2
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CHANGING THE CURRENT
L. INT. To investigate what happens to the
current when components called resistors are
placed in a circuit.
APPARATUS power supply, lamp, resistors with
different values, connecting
leads, switch and ammeter.
Vs
-

A
METHOD Build circuit using smallest resistor
and measure corresponding current. Repeat for
other resistors.
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RESULTS
RESISTOR RESISTANCE ( ) CURRENT (mA)
A 10
B 33
C 47
D 100
As the resistance increases the current decreases.
CONCLUSION
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VOLTAGE, CURRENT RESISTANCE
L. INT. To find the relationship between
voltage, current and resistance.
APPARATUS power supply, resistors, connecting
leads, switch, ohmmeter, voltmeter and
ammeter.
Vs

-
A
Circuit 1
V
Circuit 2
METHOD Measure value of resistors using circuit
1. Put smallest resistor into circuit 2,
measure current and voltage. Repeat for other
resistors.
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RESULTS
Resistor R ( ) V (V) I (A) V/I
A
B
C
D
CONCLUSION
V I x R
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RESISTANCE OF A TORCH BULB
L. INT. To investigate how the resistance of a
torch bulb varies when the brightness
changes APPARATUS power supply, bulb,
voltmeter, ammeter, connecting leads. METHOD
Build circuit Set supply
at 2v Measure current voltage Record in table
repeat for different voltages
Vs

-
A
V
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RESULTS
POWER SUPPLY (v) Voltage across bulb (V) Current (A) Resistance ( )
2 0.71 0.51 1.4
4
6
8
10
12
CONCLUSION
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RESISTANCE OF A THERMISTOR
A thermistor is a temperature dependent
resistor. L. INT. To find out how the thermistor
varies with temperature APPARATUS thermistor,
ohmmeter, hot cold water METHOD (i) connect
thermistor to ohmmeter (ii) place
thermistor in cold water, record resistance
(iii) place thermistor in hot water, record
resistance RESULTS CONCLUSION
Water Resistance ( )
Cold
Hot
As the temperature increases the resistance
decreases.
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RESISTANCE OF AN LDR
An LDR is a light dependent resistor. L. INT.
To find out how the LDR varies with
light APPARATUS LDR, ohmmeter, METHOD
(i) connect LDR to ohmmeter (ii)
place LDR in the dark, record resistance
(iii) place LDR in the light, record
resistance RESULTS CONCLUSION
Light level Resistance ( )
Dark
Light
As the light level increases the resistance
decreases.
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POWER, ENERGY TIME
To find the ENERGY used by an electrical
appliance we need to know the POWER RATING of the
appliance and the TIME the appliance is on. The
energy can be found by multiplying the power by
the time- Where E energy (J)
P power (W) T
time (s)
E P x T
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POWER , CURRENT VOLTAGE
LEARNING To investigate the relationship
between POWER, INTENTION CURRENT VOLTAGE.
APPARATUS power supply, lamps ( different
power ratings ), ammeter, voltmeter
connecting leads.
Vs
METHOD
Build circuit using 24W lamp. Switch on and
record current and voltage. Repeat
for 36W lamp.

-
A
V
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RESULTS
LAMP RATING (W) VOLTAGE (V) CURRENT (A) CURRENT X VOLTAGE
24 12 2 24
36 12 3 36
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CONCLUSION By comparing the first and last
column we have shown that the POWER equals the
CURRENT multiplied by the VOLTAGE.
P I x V
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MEASURING CURRENT 2
LEARNING To build a parallel circuit and
measure the INTENTION current at different
points in the circuit.
APPARATUS power supply, 2 bulbs,
connecting leads,
switch and ammeter
.
.
-
.
A
B
C
METHOD Build circuit and measure
current at points A, B and C
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RESULTS
POSITION CURRENT (A)
A 0.24 0.16
B 0.12 0.05
C 0.12 0.11
CONCLUSION the current at A equals the sum of
the currents at B and C
IA IB IC
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MEASURING VOLTAGE 2
LEARNING To build a parallel circuit
and measure the INTENTION voltage across bulbs 1
2 and Vs
APPARATUS power supply, 2 bulbs,
connecting
leads, switch and voltmeter.
Vs
METHOD Build circuit and measure voltage
across both lamps.
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RESULTS
supply voltage 5V
bulb 1 5V
bulb 2 5V
CONCLUSION Supply voltage equals the voltage
across bulb 1 which equals the voltage across
bulb 2
Vs V1 V2
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FAULT FINDING
Two common electrical faults are open circuits
and short circuits. As every electrical
component, from a lamp to a piece of wire, has a
resistance, we can use this knowledge to identify
such faults using an ohmmeter. OPEN CIRCUIT
the ohmmeter reads infinity as this is the
result of a broken wire or a burnt out
element. SHORT CIRCUIT the ohmmeter reads
a value that is less than expected for that
component, as its the result of a touching
wire.
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RESISTANCE IN SERIES
LESRNING To investigate how the individual
resistors INTENTION compare with the total
resistance in a series circuit APPARATUS
resistors, ohmmeter connecting leads METHOD
measure each resistor individually
connect them in series measure total
resistance RESULTS CONCLUSION
RT R1 R2
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RESISTANCE IN PARALLEL
LEARNING To investigate how the individual
resistors INTENTION compare with the total
resistance in a parallel
circuit APPARATUS resistors, ohmmeter
connecting leads METHOD measure each
resistor individually connect them in
parallel measure total
resistance RESULTS CONCLUSION
1/RT 1/R1 1/R2
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CONSUMER UNIT
The consumer unit contains the fuses or circuit
breakers that protect the mains wiring.
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Kilowatt-hour
Electricity companies charge their customers for
each unit of electricity used. 1 unit of
electricity is equal to 1Kilowatt-hour (1KWh),
which is the amount of energy a 1KW appliance
uses in 1 hour. It can be calculated using E P
x t. If power is in KW and time in hrs then E
will equal the number of units used.
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RING MAIN

• The power sockets in a house are connected by
  means of a ring circuit. There are 2 paths to
  each socket which means half the current in 1
  path and half in the other. The cables are
  thinner and therefore cheaper and less heat is
  produced in them.

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ELECTROMAGNET
An electromagnet is simply a coil of wire which
is wrapped around a soft iron core. When the wire
is connected to a power source a magnetic field
is created and the iron core acts like a
permanent magnet. The strength of an
electromagnet can be increased by using more
turns of wire or a larger current.
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ELECTRIC MOTOR
When a current flows along a wire which is in a
magnetic field, the wire experiences a force,
causing it to move (see crocodile physics).
Rotation of motor can be changed by changing the
direction of current or the direction of the
magnetic field.
Commutator reverses current multi-segment
commutators give smoother rotation brushes allow
current to flow into commutator.
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Commercial motor
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