CIE A Level Physics (9702) 2019-2021

Revision Notes

23.2.1 Electronic Sensors in Potential Divider Circuits

Properties of an Electronic Sensor

  • An electronic sensor is made up of:
    • A sensing device (LDR, thermistor, strain gauge)
    • A circuit that provides an output registered as a voltage
  • Devices which perform an “input” function are called sensors since they ‘sense’ a change in the physical environment ie. light and convert these into an electrical signal
  • These can be either:
    • Analogue sensors (produce a continuous output voltage)
    • Digital sensors (produce a binary, non-continuous output voltage)

Potential Divider Circuits with Sensory Resistors and Strain Gauges

  • Strain gauges and sensory resistors are used in potential divider circuits to vary the output voltage
  • This could cause an external component to switch on or off depending on its surroundings eg. a garden light switching on automatically after sunset

 

  • Recall that the resistance of an LDR varies with light intensity
    • The higher the light intensity, the lower the resistance and vice versa
  • The resistance of a thermistor varies with temperature
    • The hotter the thermistor, the lower the resistance and vice versa
  • The resistance of a metal-wire strain gauge varies with extension
    • The longer the extension, the higher the resistance
    • Compression of the strain gauge lowers the resistance
  • From Ohm’s law (V = IR), the potential difference Vout from a resistor in a potential divider circuit is proportional to its resistance
    • If an LDR, thermistor, or strain gauge’s resistance decreases, the potential difference through it also decreases
    • If an LDR, thermistor, or strain gauge’s resistance increases, the potential difference through it also increases

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Go to Top