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Summary Grade 9 Technology Circuits Term 3 South Africa
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A short summary on circuits and electricity with diagrams and calculations for Grade 9 Technology in Terms 3.
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Technology: Term 3 NotesElectricity:
An electrical current is a flow of charge in a conductor, and that a current flows
only when there is a complete pathway (circuit) without any gaps.
The best conductors are metals. A current can also be carried in certain liquids.
,Name Symbol Main task in circuit
Cell Energy source in an electrical or
electronic circuit.
Each cell is assumed to be 1,5V
unless otherwise stated.
Battery (series) Energy source with a higher
voltage.
When we draw circuit diagrams,
we show the cell/ battery on the
left with the positive terminal ‘on
top’.
Switch Opens (OFF) to stop electrical
energy to flow or closes (ON) to
allow electrical energy to flow in a
circuit
Conductor Carries electrical energy around a
circuit
Lamp/ Light bulb Converts electrical energy into
light energy.
Incidentally light bulbs also create
heat energy.
Light-emitting diode A control device that allows
(LED) current to flow in one direction
only (polarity) and emits light.
Resistor A resistor is a device that limits
current flow in a circuit.
Resistors heat up as they limit the
current flow.
Measured using an ohmmeter.
Diode A diode is a semi-conductor
device that will only allow current
, to flow in one direction.
Transistor A specific control device.
Input voltage to the base causes
the transistor to ‘switch on’ and
this allows current to flow through
the collector – emitter junction.
Light Dependent Resistor Resistor whose resistance
LDR Photoresistor increases or decreases depending
Photocell on the amount of light intensity.
Photoconductor Some of the uses of the LDR:
light meters used for photography
and sport light level checking. To
turn streetlights on at night and
off in the morning.
Capacitors A capacitor is a device which
stores and release electric
charge(energy).
Used to smooth the flow of
current in circuits.
Capacitors vary in shape and size.
Thermistor An electronic device that can
sense the temperature of its
environment.
Combination of words “thermal”
and “resistor”.
Uses of the thermistor:
To display the temperature of car
engines. To turn cooling fans on
and off on engines.
Buzzer
Ammeter Used to measure current at a
particular point in the circuit.
Connected in the circuit in series.
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