properties of magnets

Magnets attract these materials in addition to other magnets:

Iron cobalt nickel

How to demonstrate that something is a permanent magnet

You need to demonstrate that it can REPEL another permanent magnet

Earths north geographic pole is a..

South-seeking pole

Earths south geographic pole is a..

North-seeking pole

If you were to use a compass to figure out what the North Pole of a magnet was, how pull you do it?

The compass needle will point away from the North Pole (repels), and will point towards the South Pole

What is a magnetic field?

A regional of space in which magnetic forces act on magnets or magnetic materials

How to correctly draw magnetic field lines

Arrows point from north → south (direction of force on a free north pole, at N, it would be repelled.

Lines cannot cross each other

Lines are closest together where field is strongest

Iron filings

In presence of a magnet, iron filings become induced magnets and induce poles. These poles alone along the magnetic field of the magnet, showing the field lines.

This method does not indicate which end of the magnet is north or south

Plotting compass

Compass can be used to trace field lines. Compass needle will align with magnetic field lines (N → S)

This method does not show strength of the field

Soft and hard magnetic materials

Soft magnetic materials: easy to magnetise but also easily lose magnetisation (IRON)

hard magnetic materials: difficult to magnetise but also cannot be easily demagnetised. (STEEL)

Hard vs soft uses

Soft: core of electromagnet, needs to be able to switch off and soft magnetic materials can demagnetise easily.

Hard: compass needle, fridge magnet, loudspeaker magnet: all these things must retain magnetism (permanent magnets)

What can make a magnet demagnetise?

Heating or hitting

Induced magnetism

Bringing a permanent magnet next to unmagnetised, magnetic material makes that material an induced magnet.

There is always a force of attraction between the two, never repulsion.

So for example bringing the north pole of a magnet to the material, causes the closest surface to become a south pole.

How to make permanent magnet

If an unmagnetised sample of hard magnetic material is placed in a strong magnetic field (e.g inside a solenoid), then magnetic poles are induced onto the ends of the sample.

Once magnetised, the sample retains its magnetisation.