AQA AS Phys Unit 1- I/V Characteristics

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Current/Voltage Graphs

The term 'I/V characteristic' refers to a graph which shows how the current (I) flowing through a component changes as the potential difference (V) across it is increased. The shallower the gradient of this type of graph, the greater the resistance of the component. A curve in the graph shows resistance is changing. An I/V graph is obtained for a circuit by measuring variation of current with p.d. for a component. This is done by using either of the following;

• A potential divider to vary the p.d. from zero
• A variable resistor to vary the current to a minimum

Side note: Circuit diagrams can be found for both of these circuits on page 53 of the AQA Physics A AS textbook by Nelson Thornes.

Metallic conductor

At constant temperature, the current through a metallic conductor is directly proportional to the voltage. The characteristic graph for a metallic conductor is a straight line and this shows that resistance is constant. Metallic conductors are therefore ohmic as they have a constant resistance provided that their temperature doesn't change.

Filament lamp

The characteristic graph for a filament lamp is a curve which begins shallow, then goes steep and then shallow again as…