electricity resistance, power and energy g9-p
DESCRIPTION
A set of slides created to teach Electricity Resistance, power and energy G9-P to learners at Bishops Diocesan College in Cape Town.TRANSCRIPT
Electrical Circuits G9
K Warne
V
V1 V2
V1 = 1.5 V V2 = 1.5 V
Vsupply= 3 v
1.5 + 1.5 = 3
V1 + V2 = Vcircuit = Vcell
V
R1 R2
VC = 3 V
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Electrical cells
1.5V
One cell Battery (more than one cell)
3 cells connected in SERIES - (+)
side connected to (-) of next cell –
GIVES HIGHER VOLTAGE
+ -
Battery – cells connected in
parallel – (+) to (+) – SAME
VOLTAGE LASTS LONGER
4.5V
(1.5+1.5+1.5)
1.5V
Measuring Current
The Ammeter: • is connected in ………………… in the circuit (the current
flows through it) • has a …………………… resistance • Is connected positive to ……………. - negative to ……………..
Circuit Symbol:
An ………………. measures the ………….. flowing through the circuit.
+
_ Ammeter
…. 0.0001
The current is the ……………… of ……………….. passing a point in one ………………………. The symbol for current is “…” the unit is ……. (…).
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Measuring Current. When measuring the current through a ……………….,
the ammeter is always ………………………….. with
that component (in the …………………… as it).
A
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Measuring Potential
The Voltmeter:
• is connected in ……………..to another component in the circuit (the current does NOT flow through it)
• has a …………………resistance • Is connected positive to …………………- negative to
…………………………….
A Voltmeter measures the POTENTIAL (…………..) of the current flowing through the circuit.
+ _
Voltmeter
V 1.50
Resistor
V
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Measuring Voltage.
When measuring the voltage across a component, the voltmeter is always
connected in parallel with (or across) the component.
We measure the voltage using a device called an voltmeter. In a circuit
this is given the symbol
The voltage supplied by the battery is shared between all the
components in a series circuit
This is still
a SERIES
circuit.
V3
V2
V1
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A
V
component
here
R
Measuring Voltage - across a resistance or a bulb
Voltage is measured by connecting the voltmeter across
(or in parallel) with the component.
Voltage is measured in volts and the symbol for this is V.
V
Components
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1. Set up the circuit as shown above.
2. Connect the voltmeter across the power supply and measure the supply
voltage.
3. Then connect the voltmeter across the resistance (R) and measure this voltage.
4. Write down what you have observed:……………………………
……………………………………………………………………….
Experiment: Measuring Voltage
R
V
V
Circuit 1
Voltage cell:………..
Voltage circuit:…………………..
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Vsupply = Vcircuit
The supply voltage is equal to the voltage drop across the whole circuit.
NO ELECTRIC POTENTIAL IS LOST IN THE CONDUCTING WIRE.
Experiment: Circuit & cell Voltage
R
V
V
Circuit 1
Voltage cell: Vsupply
Voltage circuit: Vcircuit
Voltage circuit: = Voltage of supply
Vsupply = Vcircuit
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1. Set up the circuit as shown above in circuit 1.
2. Measure the voltage of the cell and circiut and current as shown.
3. Now close the switch as in circiut 2. Repeat your measurements.
4. Write down what you have observed:……………………………
……………………………………………………………………….
Open & Closed Circuit
R
V
V
Circuit 1 Voltage
cell:
Voltage circuit
R
V
V
Circuit 1 Voltage
cell:
Voltage circuit
A A
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Open & Closed Circuit
R
V
V
Circuit 1 Voltage
cell:
Voltage circuit
R
V
V
Circuit 1 Voltage
cell:
Voltage circuit
A A
Results
Circuit 1: OPEN CIRCUIT Circuit 2: CLOSED CIRCUIT
Supply Voltage
Voltage R1
Current
Supply Voltage
Voltage R1
Current
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V1
V2
V3
Voltmeter Voltage
(V)
V1
V2
V3
Experiment: Voltages in parallel
1. Set up the circuit as shown.
2. Measure all the voltages and record them
in the table.
3. Write down what you have
observed:………………………………….
………………………………………………
………………………………………………
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Circuit2
R1
V
V1 V2
Circuit2
R2
Measure the voltages indicated in the diagram and note what you
observe: …………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
……………………………………………………………………………………
V1:……………… V2:………………
Vsupply: ………………
V1 + V2 = ……………
Experiment: Voltages in series
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Experiment: Current in a series circuit
1. Set up the circuit as shown
above in circuit 1.
2. Measure the current using the
ammeter at positions 1 and 2.
3. Note down what you observe:
………………………………………..
………………………………………..
………………………………………..
R1
1
2
A
Circuit 1
A
R1 R2 3
4
5 A
A A
Circuit 2
1. Add another resistor into the
circuit as in circuit 2.
2. Now measure the current
using the ammeter at
positions 3, 4 and 5.
3. Note down what you
observe.
……………………………………..
………………………………………
……………………………………..
……………………………………..
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X X
X
A1 A2
WIRE
THICKNES
S LENGTHS
CURRENT
(mA)
BRIGHTNESS
NICHROME 0.2 1 180 BRIGHT
2 140 DIMMER
3 120 NO LIGHT
4 100 NO LIGHT
0.4 1 200 BRIGHT
2 180 DIM
3 180 DIM
4 180 NO LIGHT
Length vs Resistance
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Energy in Circuits
This section deals with the energy transfers in electric
circuits.
The most important thing to understand about energy is
that it cannot be created or destroyed.
In all devices and machines, energy is transferred from
one type to another.
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lamps
When this circuit is connected, chemical energy
stored in the battery is transferred via electrical
energy to heat and light energy in the bulbs.
The total amount of heat and light energy is the
same as the amount chemical energy lost from
the battery.
Energy Transfer in Electrical Circuits
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Energy Efficiency
We can work out the efficiency of an energy
transfer:
%Efficiency = x 100
For the bulb
efficiency =......................................
.............. energy input
..............energy output
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© Boardworks Ltd 2001
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For FULL presentation click HERE >> ScienceCafe
Hi -
This is a SAMPLE presentation only.
My FULL presentations, which contain loads more slides (with all the gaps filled in) as well as
other resources, are freely available on my resource sharing website:
www.sciencecafe.org.za
(paste into your browser if link above does not work)
Have a look and enjoy!
Keith Warne