A student investigates how the number of turns of wire on an electromagnet affects its magnetic strength.
The student passes a constant current through a copper wire wrapped around a soft iron cylinder and uses it to pick up small steel tacks.
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 | Number of steel tacks picked up |
|---|---|
| 5 | 6 |
| 10 | 12 |
| 15 | 18 |
| 20 | 24 |
| 25 | 30 |
Describe the relationship shown by these results.
Predict how many steel tacks the electromagnet will pick up if it is wound with 35 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.