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Magnetic fields
- A magnetic compass is a tiny magnetic needle pivoted at its centre. One end of the compass is always north and the other is always south due to the Earth's magnetic field.
- Like poles repel. Unlike poles attract
- Iron, steel, cobalt and nickel objects can be magnetised and demagnetised.
- Permanent magnets are made of steel because they don't lose their magnetism easily.
- Iron filings form a pattern of lines on a magnet, representing the magnetic field. The filings would be more concentrated at the poles over anywhere else on the magnet because that is where the field is the strongest. The direction of a line of force is always north to south. The greater the distance a magnet is from a plotting compass, the weaker the magnet.
- Unmagnetised materials are put in a magnet field to magnetise them. The magnetic field induces magnetism in the material. Induced magnetism causes a force of attraction between any unmagnetised magnetic material placed near one end of a bar magnet. The force is always an attractive force whichever end of the bar magnet is nearest the material
This is the basis in I/GCSE physics, make sure you understand it well before proceeding! 👩🏫
Magnetic fields of electric currents
- When a current passes through a wire, a megnetic field surrounds the wire. The lines of force caused by a straight current-carrying wire are a series of conc. circles, centred on the wire in a plane that is perpendicular to the wire
- Reversing the direction of the current reverses the direction of the magnetic field
- A solenoid is a long coil of insulated wire. They're used in devices where a strong magnetic field needs to be made. The magnetic field is made in and around the solenoid when a current is passed through the wire. The magnetic field:
- increases its strength if the current's increased
- reverses its direction if the current is reversed
- Inside the solenoid the magnetic field in a solenoid is strong and uniform
- Outside the solenoid the magnetic field lines bend around from one end of the solenoid to the other. The magnetic field outside is like the field of a bar magnet, except that each field like's a complete loop because it passes through the inside of the solenoid
- An electromagnet is a solenoid in which the insulated wire's wrapped around an iron bar (core). When current passes along a wire a magnetic field's created around the wire, so the bar's magnetised. When the current's switched off, the bar is demagnetised
Electromagnets in devices
- Electromagnets are used in scrapyard cranes, circuit breakers, electric bells and relays
- An electromagnet works in a circuit breaker/electric bell/relay by attracting an iron armature which opens a switch
Reference:
https://getrevising.co.uk/revision-notes/electromagnetism-3
This is the end of the topic! Great job!
Drafted by Cherry (Chemistry)