Electrical Components (Edexcel IGCSE Physics)

Thermistors

• A thermistor is a temperature-dependent resistor
• It is represented by the following circuit symbol:

Thermistor circuit symbol

• The resistance of a thermistor changes depending on its temperature
  • As the temperature increases the resistance of a thermistor decreases and vice versa

The resistance through a thermistor is dependent on temperature

LDRs

• A light-dependent resistor (LDR) represented by the following circuit symbol:

LDR circuit symbol

• The resistance of an LDR changes depending on the light intensity on it
  • As the light intensity increases the resistance of an LDR decreases and vice versa

The resistance of an LDR is dependent on the amount of light intensity on it

• Lamps illuminate (light up) when a current flows in a circuit
• LEDs are types of diodes
  • This means they only allow current to pass in one direction through them and will only light if the current passes in that direction

• LEDs also illuminate when a current flows in a circuit (provided the LED is placed in the correct direction)
• Since both electrical components have a visual response to current, they can be used to indicate the presence of a current in a circuit

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