(P) I-V Characteristics

• The term I-V characteristics refers to a graph which shows how the current (I) flowing through a component changes as the potential difference (V) across it is increased
• Linear components have an I-V characteristic that's a straight line (e.g. a fixed resistor)
• Non-linear components have a curved I-V characteristic (e.g. filament lamp or a diode)
• 1. Set up the test circuit shown below

  
• 2. Begin to vary the variable resistor. This alters the current flowing through the circuit and the potential difference across the component

  
• 3. Take several pairs of readings from the ammeter and voltmeter to see how the potential difference across the component varies as the current changes. Repeat each reading twice to get an average pd at each current

  
• 4. Swap over the wires connected to the battery, so the direction of the current is reserved

  
• 5. Plot a graph of current against voltage for the component
• 6. The I-V characteristics you get for an ohmic conductor, filament lamp and diode should look like these:

  
• Ohmic conductor: The current through an ohmic conductor (at constant temperature) is directly proportional to potential difference so you get a straight line

  
• Filament lamp: As the current increases, the temperature of the filament increases, so the resistance increases. This means less current can flow per unit pd, so the graph gets shallower - hence the curve

  
• Diode: Current will only flow through a diode in one direction as shown. The diode has very high resistance in the reverse direction

  
• Since V=IR, you can calculate the resistance at any point on the I-V characteristic by calculating R=V/I
• This type of circuit uses direct current (dc) and is a series circuit