4.1 Simple Phenomena Of Magnetism Flashcards
Magnetic forces are due to ___________
Magnetic forces are due to interactions between magnetic fields.
Describe the force between magnets and magnetic materials
Magnets attract magnetic materials by inducing (permanent or temporary) magnetism in them.
Difference between magnetic material and non magnetic material
magnetic material can be magnetised and is attracted to magnet
opposite for non magnetic material
Describe induced magnetism
Permanent magnets remain magnetized. They can attract unmagnetized ferrous material and magnetize them.
When the pole of the magnet is brought close to the material, that end of the material becomes the opposing pole.
When the permanent magnet is removed, the material will return to unmagnetized state or retain small amount of magnetism
Identify types of ferrous material, describe them, give an example and their usage
Hard ferrous material: hard to magnetise but retains magnetism well, e.g. hard steel, used for permanent magnets ( compass needles, loudspeaker magnets)
Soft ferrous material: easy to magnetise but readily loses magnetism, e.g. soft iron, used for core in transformer
Name the methods of magnetization
1st method: A piece of the material may be stroked with a permanent magnet from one end to the other without going in the reverse direction
* 2nd method: Place material in a strong magnetic field produced by an electromagnet (coil of wire) connected to a battery or power supply. A steady direct current flows through it, producing a magnetic field inside the coil and hence magnetises the material.
3rd method: Hammering the material in a magnetic field
Name the methods of demagnetization
1st method: Hammer the magnet at east-west direction
* 2nd method: Place the magnet in the field of an electromagnet that is connected to an alternating current supply. The magnetic field will vary back and forth. Gradually reduce the current to 0.
3rd method: Heat the magnet till temperature goes above a certain temperature.
How to determine the pattern of the field lines
Iron filings can show up the pattern of the magnetic field around the magnet. Place the magnet under a stiff sheet of plain paper or clear plastic paper and sprinkle filings over the paper or plastic. Tap the paper/plastic to allow the filings to move slightly so they line up in the field.
How to determine the pattern and direction of field lines
Place bar magnet in the centre of sheet of paper and draw around it. Place plotting compass near one of the poles and mark two dots to indicate two ends of the compass needle.
Move compass away and position it so one end of the needle is at the 2nd dot. Mark dot 3 on the other end. Repeat
until you have moved to the opposite pole of the magnet.
Draw a smooth line through the dots. This line is the field line.
Repeat the process, starting at a different point to obtain another field line.
Permanent Magnets VS Electromagnets
Permanent Magnet
Design: Hard Magnetic Material
Use: For applications where magnetism is needed over long periods (e.g. fridge doors)
Electromagnet
Design: Uses a solenoid (coil of copper wire) to create magnetic field.)
Use: For applications where magnetic field needs to be turned on and off (e.g. scrap metal moving)