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Current-Potential
Difference Graphs
Aim: To explain the graph shapes which
show how current changes as voltagechanges in electrical components.
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Starter
Draw a circuit diagram showing a battery
of two cells and a resistor.
Add an ammeter and a voltmeter to
measure current and voltage across theresistor.
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Starter
V
A
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Current-Potential Difference Graphs
We can plot a current-potential difference
graph for an electrical component if we
measure them and draw a graph.
Voltage, or potential difference, is the
independent variable we change this by
altering the number of cells in a battery.
Current is the dependent variable we
measure the effect that voltage has on it.
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Current-Potential Difference Graphs
Prediction
Make a prediction how do you think thecurrent will change as the voltage
changes?
Why do you think this?
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1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
1.4V
0.22A
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1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
2.7V
0.44A
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1.5V1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
4.3V
0.68A
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1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
5.9V
0.94A
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1.5V1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
7.3V
1.16A
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Current-Potential Difference Graph
- Resistor
Draw a graph to show the results.
Voltage
Current
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1.5V
-1.4V
-0.22A
What if you turn the battery round?
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What if you turn the battery round?
Voltage
Current
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Why is the graph this shape?
As the voltage increases the currentincreases proportionally.
This is because the electrons are movingfaster because they are being given moreenergy.
When you turn the battery round theelectrons move in the opposite direction.
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Why is the graph this shape?
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1.5 V
Decrease
voltage
Increase
voltage
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Why is the graph this shape?
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3 V
Decrease
voltage
Increase
voltage
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Why is the graph this shape?
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4.5 V
Decrease
voltage
Increase
voltage
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1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
1.4V
0.30A
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1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
2.7V
0.55A
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1.5V1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
4.3V
0.90A
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1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
5.9V
1.05A
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1.5V1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease
voltage
Increase
voltage
7.3V
1.10A
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Current-Potential Difference Graph
- Filament lamp
Draw a graph to show the results.
Voltage
Current
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What if you turn the battery round?
Voltage
Current
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Why is the graph this shape?
As the voltage increases the currentincreases.
BUT the current increase gets smaller as
the voltage gets larger. Why? This is because the filament is heating up.
The particles in the filament are vibrating
more, meaning they get in the way of theelectrons flowing through.
This slows the electrons down resistance.
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Why is the graph this shape?
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Why is the graph this shape?
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Current-Potential Difference Graph
- Diode
Sketch the graph for these results
Voltage (V) Current (A)
7.9 97.5
6.4 76.74.9 55.9
2.4 21.3
1.4 7.3
0.9 5.50.1 0.0
-1.9 0.0
-6.4 0.0
-8.9 0.0
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Current-Potential Difference Graph
- Filament lamp
Draw a graph to show the results.
Voltage
Current
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Why is the graph this shape?
As the voltage increases the current
increases.
There are no negative values because
current can only flow one way in a diode.
The line is very steep because current can
flow very quickly in the correct direction.
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Knowledge Check
What happens to current as you increase voltage?
A It stays the same
B It increases
C It decreases
Why? The electrons are being
given more energy
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Knowledge Check
Which is the correct current-potential difference
graph for a resistor?
Voltage
Current
Voltage
Current
Voltage
Current
A B C Why?
- Current increases proportionally to potential difference
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Knowledge Check
Which is the correct current-potential difference
graph for a filament lamp?
Voltage
Current
Voltage
Current
A B C
Voltage
Current
Why?
- Current doesnt increase as fast when the lamp gets warm at a high voltage.
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Knowledge Check
Why does resistance increase in a filament lamp
as you increase the voltage?
A Electrons move slower when voltage increases.
B Electrons move slower at high temperatures.
C Particles in the wire vibrating bump into the
electrons and slow them down.
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Knowledge Check
Which is the correct current-potential difference
graph for a diode?
Voltage
Current
Voltage
Current
A B C
Voltage
Current
Why?
Current only flows in one direction It flows very fast in this direction