A student investigates how the number of turns on a solenoid affects the number of paperclips it can hold.
Table
| Number of turns | Current (A) | Number of paperclips held |
|---|---|---|
| 10 | 1.0 | 3 |
| 20 | 1.0 | 6 |
| 30 | 0.8 | 7 |
| 40 | 0.6 | 7 |
The student concludes that adding more than 30 turns has no effect on the strength of the solenoid.
Why is this conclusion not valid?
The current fell as the turns increased, so the test was not fair
Each reading was taken only once, so the results are not precise
The paperclips were too heavy, so the solenoid could not hold more
The number of turns was changed, so the test was not a fair test
44 exam-style questions on OCR GCSE Physics 4.1 Magnets and magnetic fields, covering 4.1.1 Magnetic poles, attraction and repulsion, 4.1.2 Permanent and induced magnets, 4.1.3 The magnetic field of a magnet, 4.1.4 Compasses and the Earth's magnetic field, 4.1.5 The magnetic field around a current-carrying wire, 4.1.6 Field strength, current and distance, and 4.1.7 Solenoids and electromagnets. Each one has a worked solution and a mark scheme showing where the marks go.