Quick answer: Current is the flow of charge in amperes, potential difference is the energy per coulomb in volts, and resistance in ohms is the opposition to current. This Physics 9-10 lab on ohm's law gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
How does the resistance of a thermistor change as it warms up? In this lab you heat a thermistor in a water bath, measure its resistance with a multimeter, and decide what type of thermistor it is.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE P2, IGCSE 4.3
Aim
To investigate how the resistance of a thermistor changes with temperature and to decide what type of thermistor it is.
Equipment
- 10 kΩ NTC thermistor sealed in a waterproof probe, or a bare thermistor in a thin test tube
- Digital multimeter with an ohm range
- Beaker of at least 250 mL
- Kettle or hot water and some cold water or ice
- Thermometer reading to 1 °C
- Stirrer and a stopwatch
Safety
Hot water can scald. Pour it carefully and let an adult handle a kettle. Keep the multimeter and its leads dry and never use it on mains electricity. Wipe up spills at once.
Method
- Place the thermistor in a test tube and stand the tube in a beaker of water at about 20 °C.
- Connect the multimeter leads to the thermistor leads and set it to the ohm range.
- Stir, wait 60 seconds, then record the temperature and the resistance.
- Add a little hot water and stir. Wait until the temperature is steady and record again.
- Repeat in steps of about 10 °C up to about 70 °C.
- Let the water cool and record again on the way down to check the readings.
Results
Sample measurements:
| Temperature (°C) | Resistance (kΩ) |
|---|---|
| 20 | 12.54 |
| 30 | 8.04 |
| 40 | 5.30 |
| 50 | 3.59 |
| 60 | 2.49 |
| 70 | 1.76 |
Analysis questions
Question 1 Plot the graph
Plot resistance (y-axis) against temperature (x-axis) and draw a smooth curve through the points.Question 2 Describe the pattern
Describe how the resistance changes with temperature, and state the type of thermistor.Question 3 Percentage change
Calculate the percentage fall in resistance from 20 °C to 70 °C.Question 4 Interpolate
Estimate the temperature at which the resistance is 5.0 kΩ.Question 5 Current in a circuit
The thermistor is joined to a 6.0 V supply. Calculate the current at 20 °C and at 70 °C.Question 6 Sources of error
Suggest two reasons the readings might differ from the true values.Question 7 Improvement
Suggest two improvements to the method.
