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.