Biology paper1

• Investigating the current-voltage characteristics of circuit components

  1. Use a circuit with a battery, resistor, ammeter, variable resistor, and voltmeter

  2. Measure potential difference across resistor and current through resistor

  3. Adjust variable resistor and record new readings

  4. Repeat for a range of readings

  5. Reverse battery direction and repeat measurements
• Current through a resistor

  Directly proportional to potential difference across resistor
• Resistor


  • Ohmic conductor
  • Relationship between current and potential difference is linear and passes through the origin
• Temperature of resistor must be kept constant, otherwise the graph will not be linear
• Investigating the current-voltage characteristics of a filament lamp

  1. Use a circuit with a battery, filament lamp, ammeter, variable resistor, and voltmeter

  2. Measure potential difference across lamp and current through lamp

  3. Adjust variable resistor and record new readings

  4. Repeat for a range of readings

  5. Reverse battery direction and repeat measurements
• Current through a filament lamp

  Not proportional to potential difference across lamp
• Filament lamp


  • As current increases, temperature of filament increases, causing resistance to increase
  • Graph of current vs potential difference is not linear
• Investigating the current-voltage characteristics of a diode

  1. Use a circuit with a battery, diode, extra resistor, ammeter, variable resistor, and voltmeter

  2. Measure potential difference across diode and current through diode

  3. Adjust variable resistor and record new readings

  4. Repeat for a range of readings

  5. Reverse battery direction and repeat measurements
• Current through a diode

  • Only flows when potential difference is around 0.6-0.7 V
  • No current flows when potential difference is reversed
• Diode


  • Has high resistance in reverse direction to protect against high currents
• This is a required practical, so it's important to learn the details