Quick answer: Static electricity is electric charge that builds up on insulators when electrons are transferred by rubbing. This Physics 9-10 lab on static electricity 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 amount of charge on a plastic strip depend on how many times you rub it? In this lab you charge a strip, hold it over tissue-paper bits and count how many it lifts, then analyse the pattern.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE P2, HS-PS2-4
Aim
To investigate how the number of rubbing strokes affects the amount of charge on a plastic strip, using the number of tissue-paper bits it lifts as a measure.
Equipment
- Strip of polythene (a strip cut from a clean carrier bag, or a plastic ruler)
- Woollen cloth or dry paper towel
- Tissue paper cut into 5 mm squares (about 30 pieces)
- Tray or flat plate
- Ruler
- Notebook and pencil
Safety
Work away from water, electric sockets and flammable liquids. Use a dry room because damp air lets charge leak away. Brush the paper off your hands before touching your face.
Method
- Spread the same 30 paper bits on the tray each time.
- Wipe the strip clean and rub it along the cloth 10 times in one direction only, always at the same speed.
- Hold the strip 2 cm above the paper bits, without touching them, for 5 seconds.
- Count how many bits are lifted and stick to the strip.
- Touch the strip with your hand to remove its charge, then repeat the test two more times with 10 rubs.
- Repeat the whole procedure for 20, 30, 40 and 50 rubs.
Results
Sample measurements (number of paper bits lifted):
| Number of rubs | Trial 1 | Trial 2 | Trial 3 | Mean |
|---|---|---|---|---|
| 10 | 2 | 3 | 2 | 2.3 |
| 20 | 5 | 4 | 6 | 5.0 |
| 30 | 8 | 9 | 8 | 8.3 |
| 40 | 11 | 10 | 12 | 11.0 |
| 50 | 12 | 12 | 13 | 12.3 |
Analysis questions
Question 1 Plot the graph
Plot the mean number of bits (y-axis) against the number of rubs (x-axis) and draw a smooth curve.Question 2 Describe the trend
Describe how the number of bits lifted changes as the number of rubs increases.Question 3 Why it levels off
Suggest why the increase slows down at a large number of rubs.Question 4 Control variables
Name three variables that were controlled and explain why.Question 5 Humidity
Predict the effect of doing the lab on a rainy, humid day and explain it.Question 6 Reliability
Use the spread of repeat readings to comment on reliability.Question 7 Improvement
Suggest one improvement to make the measure of charge more precise.
