Lesson 41: Magnetic Fields
Magnetic fields extend around magnets in three dimensions. Iron filings show patterns in those fields, while comparisons between magnets and electromagnets connect field strength, distance, and electric current.
Key Ideas
- The magnetic field is the invisible region around a magnet where its force can act.
- Field lines run from the North pole to the South pole. Where they bunch up close together, the field is strongest.
- A magnetic field is a three-dimensional shape surrounding a magnet on every side, not a flat pattern.
- A magnet's field is strongest right at its surface and fades quickly with distance, until it's too weak to feel.
- Two magnetic fields combine into one: they strengthen each other when opposite poles face, and push apart when matching poles face.
- Moving electric current also creates a magnetic field, which is how an electromagnet works, and it can be switched on and off.
Vocabulary
- Magnetic field: The invisible region surrounding a magnet where its force can pull or push on magnetic materials.
- Field line: A line tracing the direction of a magnetic field, running from the North pole to the South pole. Bunched lines mean a stronger field.
- Electromagnet: A magnet made by coiling wire carrying electric current around iron, which can be switched on and off.
Discussion Questions
- A friend says only magnets have magnetic fields. Using what you built with the wire and battery, what's wrong with that claim?
- You test paper, glass, and a thick steel spoon between a magnet and a paperclip. Which one changes the pull the most, and why?
- Two magnets are placed with matching poles facing each other. What happens to the field in the gap between them, and how does that match what you feel?
Supplies
- A magnet, iron filings or finely snipped steel wool, and a sheet of paper
- A large iron nail, a few feet of insulated wire, a battery, and paperclips (adult supervision)
- Paper, cardboard, a piece of glass, and a thick piece of iron or steel