diodes and thermistors

• what do diodes do?

  only let current pass in one direction
• the resistance is almost zero when the p.d goes the right way
• the resistance is enormous when the p.d goes there wrong way, so the current is zero
• some diodes emit light when the current passes through it the right way e.g. LEDs
• current-voltage graph for a diode

  
• how is a thermistor difference from most other components?

  it is made of a special material
• when the temperature rises, the resistance of the thermistor decreases