A group of students is investigating magnetic fields and electromagnetism.
A bar magnet is aligned vertically with its South pole (S\text{S}S) at the top and its North pole (N\text{N}N) at the bottom. A point QQQ is marked on a magnetic field line directly to the right of the middle of the magnet. State the direction of the magnetic field at point QQQ (choose from: upwards, downwards, to the left, or to the right).
A straight vertical wire carrying an electric current vertically upwards 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 at a point near the wire could be increased.
The students investigate how the current in a solenoid electromagnet affects the magnetic field strength at its centre by using a Hall probe to measure the field strength (in microtesla, μT\mu\text{T}μT).
Their results are recorded in the table below:
| Current (A\text{A}A) | Magnetic field strength (μT\mu\text{T}μT) |
|---|---|
| 0.0 | 0 |
| 0.4 | 12 |
| 0.8 | 24 |
| 1.2 | 36 |
| 1.6 | 48 |
| 2.0 | 60 |
Describe the appearance of the line of best fit if these data were plotted on a graph with Current on the horizontal axis and Magnetic field strength on the vertical axis.
Describe the relationship between the current and the magnetic field strength. 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 valid investigation.