Resistors

• For some resistors, the value of the resistance remains constant, but for others, the resistance changes with the current.
• The current through an ohmic conductor at a constant temperature is

  directly proportional to the potential difference across a resistor.

  Meaning that the resistance remains constant as the current changes.

  
• The resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.
• • the resistance of a filament lamp increases as the temperature of the filament increases

  
• the current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction

  
• • The resistance of a thermistor decreases as the temperature increases
  • the applications of thermistors in circuits: a thermostat
• • The resistance of an LDR decreases as light intensity increases
  • the application of LDRs in circuits: switching lights on when it gets dark