2Materials Only iron, steel, nickel and cobalt are magnetic. Bar magnets have to be made using one of these substances.
3The metals affected by magnetism consist of tiny regions called 'Domains' which behave like tiny magnets.
4Normally they are arranged in the magnetic material all pointing in different directions in a completely random fashion and so their magnetic effects cancel each other out. If an object is magnetised it is because the domains are all made to point in the same direction.
5Field lines run from North to South. CompassesField lines run from North to South.The magnetic field is strongest at the poles.Magnet
9The Earth itself has a huge magnetic field - as if it had a huge bar magnet embedded at its centre. The Earth’s magnetic field lines emerge from near the geographical north pole and re-enter it at the south pole.
10Unlike poles attract.North and South.Like poles repel.North and north.South and south
11We can plot field lines using Iron FillingsPlotting Compass
12Magnetic fieldsMagnetic fields are regions where they experience a magnetic force.You can investigate these using a plotting compass or iron filings.Like poles repel and unlike poles attract.
13Like poles are repelling so the magnet on the right is suspended in the air.
14MAGNETIC FIELD PATTERNS This diagram shows the magnetic field patterns around the unlike and like poles of a pair of magnets.
15Investigation:You are given two magnets find out which one is strongest
16Fair Testing The same size paper clip Same place – not near another magnetic field , or near another metal object.Same temperatureSame pole of magnet.Paper clips of the same metal – must not be magnetised before, not joined together.
17What I will measure.The number of paper clips in a row.
18SOME MAGNET FACTSThe poles of Earth can change. Magnetic lines of rocks laid down long ago show that once the North pole was the South pole; and the South pole the North poleYour favourite music and television programmes can be stored magnetically. Sound and video tapes are plastic ribbons with a magnetic coat. Information is recorded on the tapes as magnetic fields. Stroke them with a magnet and all this information which includes sound and pictures will be lost foreverA letter written in 1269 by the Scientist calling himself Peter the Pilgrim has the first mention of the poles of a magnetAn Alnico magnet is a combination of aluminium, nickel and cobalt, and can be very powerful.The strongest magnets are ceramic. They are made from metal powders, heated together under very high pressure
19ElectromagnetsA wire with a current in it has a magnetic field around it.The strength of a magnetic field can be increased by wrapping a wire around an iron bar
20Electromagnet A soft iron rod has no magnetic field When current flows in the wire the soft iron becomes magnetised so a magnetic field is detected by the plotting compasses.
21Hans Christian Oersted (1777-1851) Oersted’s ExperimentHans Christian Oersted ( )Hans Christian Oersted discovered in 1820 that an electric current near a compass causes the compass needle to be deflected. Oersted's experiment showed that every electric current has a magnetic field surrounding it.
23The first electromagnet was made by an English scientist called William Sturgeon in It could lift a few pins. Modern electromagnets can lift whole cars. Some are so powerful they affect metals, like copper, which are not usually magnetic.
25An electric bell also uses an electromagnet An electric bell also uses an electromagnet. See if you can describe in your own words how the bell works.
26The Earth’s magnetic field extends far into space The Earth’s magnetic field extends far into space. It is called the “magnetosphere.”The solar wind is constantly bombarding the Earth’s magnetic field. Sometimes these charged particles penetrate that field. These particles are found in two large regions known as the Van Allen Belts.When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…
27When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…The Aurora Borealis in the Northern HemisphereAnd the Aurora Australis in the Southern Hemisphere
28Only iron, steel,nickel and cobalt are magnetic. Summary of MagnetismOnly iron, steel,nickel and cobalt are magnetic.Bar magnets have to be made using one of these substances.All bar magnets have invisible magnetic fields.One end of a magnet is called the north pole – this is the side which will swing to face the Earths’ magnetic north.The field lines always point from the North pole to the South pole.All current produces magnetism.A coil of wire with a soft iron core is a good electro-magnet