Potential Divider Sensor Calibration for H2 Physics Practical: Thermistor, LDR and Vout Graphs

Q: What does a potential divider sensor practical test?
A: It tests whether you can convert a changing resistance into a measurable output voltage, then calibrate that voltage against temperature or light intensity.

TL;DR
A thermistor or LDR in a potential divider turns temperature or light level into Vout. Choose a fixed resistor near the sensor's working resistance, measure Vout against a known reference, plot a calibration graph, and use the graph to interpolate unknown values. ACE marks come from loading, self-heating, thermal lag, ambient light, and non-linear response.

Use this with H2 Physics Paper 4 spreadsheet skills, H2 Physics capacitor RC practical, and H2 Physics practical lab mastery.

Status: SEAB H2 Physics 9478 syllabus checked 2026-05-01. Topic 16 includes potential divider circuits involving NTC thermistors and light-dependent resistors. This page frames that theory as a Paper 4 style calibration skill.

1 | What A Sensor Divider Does

A potential divider has two resistive components in series. The output voltage depends on the fraction of total resistance across the output component.

If one component is a sensor:

• A thermistor changes resistance with temperature.
• An LDR changes resistance with light intensity.
• The output voltage changes as the environment changes.

The practical task is to calibrate Vout against a known reference so the circuit becomes a measuring instrument.

2 | Choosing The Fixed Resistor

The fixed resistor should be chosen for the working range.

Rule of thumb:

• Choose fixed resistance close to the sensor resistance in the middle of the range of interest.
• This usually gives better sensitivity in the useful region.
• If the fixed resistor is much too large or too small, Vout changes only weakly.

In an exam, justify the choice by referring to sensitivity and measurable voltage change.

3 | Thermistor Calibration Method

1. Place thermistor in a water bath.
2. Place a reference thermometer beside it.
3. Keep the thermistor dry if it is not waterproofed.
4. Record temperature and Vout after thermal equilibrium.

Reviewed by

Chee Wei Jie·Academic Advisor (Physics)

Practical course completion-record note

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