Electrical Components (Edexcel IGCSE Physics (Modular))

Thermistors & LDRs

• Environmental conditions, such as temperature and light intensity, can influence the resistance of resistors, such as

  • Thermistors

  • Light-dependent resistors (LDRs)

Thermistors

• The resistance of a thermistor depends on its temperature

• The resistance of a thermistor is high in cold conditions and low in hot conditions
  

  • As the temperature increases the resistance of a thermistor decreases

  • As the temperature decreases the resistance of a thermistor increases

The resistance of a thermistor depends on its temperature

• The relationship between resistance and temperature for a thermistor can be shown on a graph

The graph of resistance against temperature for a thermistor shows a curve indicating these quantities are inversely proportional to each other

Light-dependent resistors (LDRs)

• The resistance of a light-dependent resistor (LDR) depends on the light intensity on it

• The resistance of an LDR is high in dark conditions and low in bright conditions 
  

  • As the light intensity increases the resistance of an LDR decreases

  • As the light intensity decreases the resistance of an LDR increases

The resistance of an LDR depends on the intensity of light on it

• The relationship between resistance and light intensity for an LDR can be shown on a graph

The graph of light intensity against temperature for an LDR shows a curve indicating these quantities are inversely proportional to each other

Lamps & LEDs

• Lamps and light-emitting diodes (LEDs) illuminate (light up) when a current flows through them

• This makes them useful for indicating the presence of a current in a circuit

Light-emitting diodes (LEDs)

• LEDs are a type of diode

  • This means they only allow current to flow through them in one direction

  • Therefore, in a circuit, an LED will only light up if it is placed in the correct direction

• The circuit symbol for an LED is as follows:

LEDs can be used to indicate the presence of a current as they illuminate when current flows through them. The same is true for lamps