Changing resistance makes a voltage sensor
An LDR or thermistor changes resistance with the environment. A potential divider converts that resistance change into an output-voltage change.
Follow the reasoning
- Identify how the sensor resistance responds to the environment.
- Check whether output is taken across the sensor or the fixed resistor.
- Use the divider equation to predict the output change.
Try it in a past paper 2
Open the question, then use its mark scheme to check your work.
Question 3(b)
Calculate and evaluate the output of a thermistor potential divider.
Question 18
Explain how lamp resistance and voltage change in a variable-resistor circuit.
Build the supporting skills. Practise changing resistance and voltage division with a filament lamp. This is preparation for the sensor connection; it does not use an LDR or thermistor.
A curated collection checked against the question papers and mark schemes; not a complete past-paper catalogue. Links open official OCR PDFs in a new tab.
Put the ideas to work
More practice is on its way
No PhysicsUK question linked yet. New eligible questions appear here as the bank grows.
Specification outcomes (4)
- 4.2.3(c)(i) Describe and sketch I–V characteristics for resistor, filament lamp, thermistor, diode and LED.
- 4.2.3(d) Describe how the resistance of a light-dependent resistor (LDR) varies with light intensity.
- 4.3.3(b) Describe potential divider circuits with variable components such as LDRs or thermistors.
- 4.3.3(c)(i) Use potential divider equations Vout = (R₂ / (R₁ + R₂)) × Vin and V₁ / V₂ = R₁ / R₂.