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Magnets and magnetic fields
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Magnets exert forces without touching. A current in a wire also makes a magnetic field.
Magnets
Like poles repel; unlike poles attract.
A permanent magnet has its own field. An induced magnet becomes magnetic only when it is in a field, and always attracts.
Magnetic materials: iron, steel, nickel and cobalt.
A permanent magnet has its own field. An induced magnet becomes magnetic only when it is in a field, and always attracts.
Magnetic materials: iron, steel, nickel and cobalt.
Field lines
Field lines go from north to south outside the magnet.
The closer the lines, the stronger the field. A plotting compass shows the direction.
The Earth has a magnetic field, which is why a compass points north.
The closer the lines, the stronger the field. A plotting compass shows the direction.
The Earth has a magnetic field, which is why a compass points north.
Fields from currents
A current in a straight wire makes a circular field around it.
A coil of wire (a solenoid) makes a field like a bar magnet. Adding an iron core makes an electromagnet, which can be switched on and off.
More turns, more current or an iron core make the field stronger.
A coil of wire (a solenoid) makes a field like a bar magnet. Adding an iron core makes an electromagnet, which can be switched on and off.
More turns, more current or an iron core make the field stronger.
Give two ways to make an electromagnet stronger.
- Increase the current.
- Add more turns of wire, or add an iron core.
Answer: More current, more turns (or an iron core).
Like poles repel. Field lines run north to south. A current makes a magnetic field; a solenoid with an iron core is an electromagnet.
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