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 A V

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?

Current-Potential Difference Model 1.5V 0.22A Decrease voltage Increase voltage 1.4V

Current-Potential Difference Model 1.5V 1.5V 0.44A Decrease voltage Increase voltage 2.7V

Current-Potential Difference Model 1.5V 1.5V 1.5V 0.68A Decrease voltage Increase voltage 4.3V

Current-Potential Difference Model 1.5V 1.5V 1.5V 1.5V 0.94A Decrease voltage Increase voltage 5.9V

Current-Potential Difference Model 1.5V 1.5V 1.5V 1.5V 1.5V 1.16A Decrease voltage Increase voltage 7.3V

Current-Potential Difference Graph - Resistor Draw a graph to show the results. Current Voltage

What if you turn the battery round? 1.5V -0.22A -1.4V

What if you turn the battery round? Current Voltage

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? 1.5 V e e e e e e e e e e e Decrease voltage Increase voltage

Why is the graph this shape? 3 V e e e e e e e e e e e Decrease voltage Increase voltage

Why is the graph this shape? 4.5 V e e e e e e e e e e e Decrease voltage Increase voltage

Current-Potential Difference Model 1.5V 0.30A Decrease voltage Increase voltage 1.4V

Current-Potential Difference Model 1.5V 1.5V 0.55A Decrease voltage Increase voltage 2.7V

Current-Potential Difference Model 1.5V 1.5V 1.5V 0.90A Decrease voltage Increase voltage 4.3V

Current-Potential Difference Model 1.5V 1.5V 1.5V 1.5V 1.05A Decrease voltage Increase voltage 5.9V

Current-Potential Difference Model 1.5V 1.5V 1.5V 1.5V 1.5V 1.10A Decrease voltage Increase voltage 7.3V

Current-Potential Difference Graph - Filament lamp Draw a graph to show the results. Current Voltage

What if you turn the battery round? Current Voltage

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 results Voltage (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 -6.4 -8.9

Current-Potential Difference Graph - Filament lamp Draw a graph to show the results. Current Voltage

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 Current Voltage Current Voltage Why? A B C - Current increases proportionally to potential difference

Knowledge Check Which is the correct current-potential difference graph for a filament lamp? Current Current Current Voltage Voltage Voltage A B C 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? Current Voltage Current Current Voltage Voltage A B C Why? - Current only flows in one direction. It flows very fast in this direction.