A group of students is investigating magnetic fields and electromagnetism.
A bar magnet is aligned horizontally with its South pole (S\text{S}S) on the left and its North pole (N\text{N}N) on the right. A point PPP is marked on a magnetic field line directly above the top-middle of the magnet. State the direction of the magnetic field at point PPP (choose from: to the left, to the right, upwards, or downwards).
A straight vertical wire carrying an electric current vertically downwards passes through a flat horizontal card.
Describe the shape of the magnetic field lines formed on the card and state their direction (clockwise or anticlockwise) when viewed from directly above the card.
State one way the magnetic field strength around the wire could be increased.
The students investigate how the current in an electromagnet affects its magnetic strength by measuring the maximum mass of iron filings (in grams, g\text{g}g) it can lift.
Their results are recorded in the table below:
| Current (A\text{A}A) | Mass of iron filings lifted (g\text{g}g) |
|---|---|
| 0.0 | 0 |
| 0.5 | 15 |
| 1.0 | 30 |
| 1.5 | 45 |
| 2.0 | 60 |
| 2.5 | 75 |
Describe the appearance of the line of best fit if these data were plotted on a graph with Current on the horizontal axis and Mass of iron filings on the vertical axis.
Describe the relationship between the current and the mass of iron filings lifted. Use data from the table to support your answer.
Suggest two variables that the students must keep constant (control) in this experiment to ensure a fair test.