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

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01 May 2026, 00:00 Z

Reviewed by

Chee Wei Jie·Academic Advisor (Physics)

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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.