Current-Potential Difference Graphs Aim: To explain the graph shapes which show how current changes as voltage changes in electrical components.
Mar 31, 2015
Current-Potential Difference Graphs
Aim: To explain the graph shapes which
show how current changes as voltage
changes in electrical components.
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 the resistor.
Starter
V
A
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.
Current-Potential Difference Graphs
• Prediction
• Make a prediction – how do you think the current will change as the voltage changes?
• Why do you think this?
1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
1.4V
0.22A
1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
2.7V
0.44A
1.5V1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
4.3V
0.68A
1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
5.9V
0.94A
1.5V1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
7.3V
1.16A
Current-Potential Difference Graph - Resistor
• Draw a graph to show the results.
Voltage
Current
1.5V
-1.4V
-0.22A
What if you turn the battery round?
What if you turn the battery round?
Voltage
Current
Why is the graph this shape?
• As the voltage increases the current increases proportionally.
• This is because the electrons are moving faster because they are being given more energy.
• When you turn the battery round the electrons move in the opposite direction.
Why is the graph this shape?
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1.5 V
Decrease voltage
Increase voltage
Why is the graph this shape?
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3 V
Decrease voltage
Increase voltage
Why is the graph this shape?
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4.5 V
Decrease voltage
Increase voltage
1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
1.4V
0.30A
1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
2.7V
0.55A
1.5V1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
4.3V
0.90A
1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
5.9V
1.05A
1.5V1.5V1.5V1.5V1.5V
Current-Potential Difference Model
Decrease voltage
Increase voltage
7.3V
1.10A
Current-Potential Difference Graph- Filament lamp
• Draw a graph to show the results.
Voltage
Current
What if you turn the battery round?
Voltage
Current
Why is the graph this shape?
• As the voltage increases the current increases.
• 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 the electrons flowing through.
• This slows the electrons down – resistance.
Why is the graph this shape?
Why is the graph this shape?
Current-Potential Difference Graph - Diode
• Sketch the graph for these resultsVoltage (V) Current (A)
7.9 97.5
6.4 76.7
4.9 55.9
2.4 21.3
1.4 7.3
0.9 5.5
0.1 0.0
-1.9 0.0
-6.4 0.0
-8.9 0.0
Current-Potential Difference Graph- Filament lamp
• Draw a graph to show the results.
Voltage
Current
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.
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
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
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 doesn’t increase as fast when the lamp gets warm at a high voltage.
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.
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.