Final answer:
A magnetic field is produced by The Earth, a magnet, an electric current, and a moving electric charge. An ordinary piece of iron does not inherently produce a magnetic field but can become magnetized, while a stationary electric charge and an unconnected battery do not produce a magnetic field.
Step-by-step explanation:
Items that will produce a magnetic field include:
- The Earth: The Earth itself is a giant magnet with a magnetic field extending into space, which is why compasses point north.
- A magnet: This is an object that naturally produces a magnetic field, causing it to attract materials like iron.
- An electric current: Any flow of electrical charge, such as that through a wire, generates a magnetic field around it.
- A moving electric charge: As it moves, it creates a magnetic field in the surrounding space.
An ordinary piece of iron, while not inherently a magnet, can become magnetized in a magnetic field. A magnet can attract metals such as iron and is also involved in various applications, including electric motors and medical imaging like MRI.
On the other hand, an electric charge at rest (c), the voltage of a battery not connected to anything (f), or a piece of any metal (a) will not produce a magnetic field unless other conditions are met (like the metal becoming magnetized in an existing magnetic field or the electric charge moving).