Engineering & STEM
GCSE & BTEC engineering revision
Practise units, drawing tolerances and evidence recording with a worked inspection example and short self-checks for GCSE and BTEC engineering learners.
Three questions from the bench
Work each answer out on paper first. Open the explanation to check your method.
1. A 12-tooth gear drives a 36-tooth gear at an input speed of 900 rpm. What is the output speed?
Check your answer
300 rpm. The driven wheel has three times as many teeth, so the shaft runs at one third of 900 rpm.
2. A spacer must be 22.0 ± 0.1 mm long. Which reading is outside tolerance?
Check your answer
22.15 mm. The permitted range is 21.9 to 22.1 mm. At 22.15 mm, the spacer is 0.05 mm above the upper limit.
3. A 150 Ω resistor carries 20 mA. What is the voltage across it?
Check your answer
3 V. Convert 20 mA to 0.020 A, then multiply by 150 Ω to get 3 V.
Read the drawing as an instruction
A drawing specifies a spacer length of 40.0 ± 0.2 mm. The smallest acceptable value is 39.8 mm and the largest is 40.2 mm. A recorded value of 40.1 mm lies inside those limits. A value of 40.3 mm lies outside. If a reading lies very close to a limit, the instrument resolution and measurement uncertainty matter. Follow the inspection method specified for the job.
| Spacer | Measured length | Initial finding |
|---|---|---|
| A | 39.9 mm | Inside the permitted range |
| B | 40.3 mm | Above the upper limit |
| C | 40.0 mm | Inside the permitted range |
A useful inspection record includes the drawing revision, the instrument, the permitted range and the result for each part. Keep the recorded reading even when a part fails. A later investigation might ask whether one part was unusual or whether measurements drifted upwards during a batch.
Show your calculation
Write the relationship first, convert units, substitute, then label the answer. For a force of 8 N acting at right angles 250 mm from a pivot, the distance is 0.250 m. The moment is 8 × 0.250 = 2 N·m. An answer of 2,000 N·m would mean the force was applied 250 metres away. Imagining that handle helps you spot a slipped conversion.
Explain an improvement with evidence
In a practice project, a model gearbox must deliver 100–120 rpm. Three tests return 124, 126 and 125 rpm. The average is 125 rpm and every reading is above the upper limit. Identify which gear could change, predict the new output speed, then repeat the tests at the same input speed and load. A statement such as “the model worked better” leaves the reader guessing what improved.
The questions here practise transferable skills for GCSE physics and technical engineering study. For an assessed BTEC task, use the specification and brief for your own qualification. Keep notes and photographs of your own practical work. Use the circuit workbench or the gear ratio calculator to try another set of numbers.
Sources and further reading
- AQA GCSE Physics | Forces · Checked 2026-11-08
- Pearson | Engineering Tech Award qualification and specification · Checked 2026-11-08