A student investigates how the number of turns of wire wound around an iron core affects the maximum load of steel paperclips an electromagnet can support before they drop.
The student passes a constant current through a copper wire wrapped around a soft iron cylinder and measures the mass of paperclips suspended from the end of the cylinder.
Name two control variables that the student must keep constant in this experiment to ensure a fair test.
The table below shows the student's results:
| Number of turns of wire | Mass of steel paperclips supported (g) |
|---|---|
| 10 | 4.0 |
| 20 | 8.0 |
| 30 | 12.0 |
| 40 | 16.0 |
| 50 | 20.0 |
Describe the relationship shown by these results.
Predict the mass of steel paperclips the electromagnet will support if it is wound with 75 turns.
Below is a sketch of the magnetic field around this electromagnet:
State the direction of the magnetic field lines outside the electromagnet (relative to the labeled poles).
Explain how the representation of the field lines shows where the magnetic field is strongest.
Identify the region where the magnetic field is at its strongest.