Electricity
Control Circuits
To explain how thermistors and light-dependent resistors can be used to control electrical circuits.
What you will learn
How a thermistor responds to temperature
How an LDR responds to light intensity
How changing resistance affects current and voltage
How sensors can control an output component
How to explain the behaviour of a control circuit
Explanation
An NTC thermistor’s resistance decreases as temperature increases. An LDR’s resistance decreases as light intensity increases. These resistance changes alter current or share of p.d. in a circuit, allowing light or temperature sensing. Predict the output from the stated arrangement rather than assuming every sensor circuit behaves identically. Example: Predict thermistor current at 6 V when R falls from 300 Ω to 100 Ω. I increases from 0.02 A to 0.06 A using I = V/R. Give a reason. Use evidence.