Current-voltage graphs
You need to know how to investigate how current changes with voltage for a component, eg for a resistor (or wire) at constant temperature, a filament lamp and a diode.
You should be familiar with the circuit diagram and the results for the different components.
This circuit can be used to determine the relationship between the current and the voltage for different components.
The variable resistor can be adjusted in order to give a range of voltages.
The current can be recorded for each of the voltages and a graph of current against voltage plotted.
Current-voltage graphs
Take a graph where the current flow is shown on the vertical axis and the voltage is shown on the horizontal axis. This shows that as the current changes in a component, so does the voltage.
You should be able to recognise these graphs for resistors at constant temperature, for A common type of light bulb containing a thin coil of wire called the filament. and for diodes.
Resistor at constant temperature
The current flowing through a resistor at a constant temperature is directly proportional to the voltage across it. A component that gives a graph like this is said to follow The rule that states that the current (I) flowing through a resistor (R) is directly proportional to the voltage (V) across the resistor, provided the temperature remains constant..
The resistance can be calculated using this equation.
\(\text{resistance (R) =}~\frac{\text{voltage (V)}}{\text{current (I)}}\)
If the resistance is constant, doubling the voltage will double the current. We can say that the current is proportional to the voltage (this can be written as I \(\propto\) V).