Thermistors Thermistors are resistors that vary the amount of current that can pass through them depending on their temperature. The input is the temperature and the output is how much current can pass through them.
Thermistors are used in circuits for many purposes including: Digital thermometers. Systems to warn drivers that their engine is overheating. Turning off the kettle when the water starts to boil. Controlling the temperature in a house. Preventing rechargeable batteries from overheating while recharging.
l l l l l
32.2 Diodes
Activity Observing a diode in a circuit
Apparatus Diode, bulb, leads, crocodile clips, battery or power supply
Thermistor A type of
resistor where the resistance depends on temperature.
Fig. 6 The symbol for a thermistor.
Fig. 7 A diode.
Fig. 8 The symbol for a diode.
Method 1. Set up the circuit shown in the diagram in Fig. 9. 2. What do you see when the circuit is connected? 3. Switch the diode around so that it is facing in the opposite direction.
4. What do you see when the circuit is connected?
+ - 6 V
Fig. 9
Diodes are electronic components that only allow current to flow through them in one direction. They are used to ensure that the current in a circuit is only flowing in one direction. This is important as other electronic components can be damaged by current flowing in the wrong direction. The diodes protect these other components. All the components in Fig. 10 are diodes. Some give out light and some do not. When diodes are connected in a way that allows current to flow they are said to be in forward
bias. When diodes are connected in a way that does not allow current to flow they are said to be in reverse bias. Diodes have a positive and a negative end. There is usually a line or band towards the negative end, as can be seen in Fig. 7 above. Even though electrons actually flow from the negative terminal to the positive terminal,
current is said to flow from positive to negative. This is because circuit diagrams were used before scientists understood how electricity actually travels.
Diodes are electronic
components that only allow current to flow through them in one direction.
