MAGNETISM

Materials Only iron, steel, nickel and cobalt are magnetic. Bar magnets have to be made using one of these substances.

The metals affected by magnetism consist of tiny regions called 'Domains' which behave like tiny magnets.

Normally 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.

Field lines run from North to South. Compasses Field lines run from North to South. The magnetic field is strongest at the poles. Magnet

Iron Fillings-Shows field but not direction

Plotting Compass method

Final Pattern

The 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.

Unlike poles attract. North and South. Like poles repel. North and north. South and south

We can plot field lines using Iron Fillings Plotting Compass

Magnetic fields Magnetic 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.

Like poles are repelling so the magnet on the right is suspended in the air.

MAGNETIC FIELD PATTERNS This diagram shows the magnetic field patterns around the unlike and like poles of a pair of magnets.

Investigation: You are given two magnets find out which one is strongest

Fair Testing The same size paper clip Same place – not near another magnetic field , or near another metal object. Same temperature Same pole of magnet. Paper clips of the same metal – must not be magnetised before, not joined together.

What I will measure. The number of paper clips in a row.

SOME MAGNET FACTS The 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 pole Your 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 forever A letter written in 1269 by the Scientist calling himself Peter the Pilgrim has the first mention of the poles of a magnet An 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

Electromagnets A 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

Electromagnet 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.

Hans Christian Oersted (1777-1851) Oersted’s Experiment Hans Christian Oersted (1777-1851) 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.

Internet Demo

The first electromagnet was made by an English scientist called William Sturgeon in 1825. 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.

An 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.

The 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…

When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called… The Aurora Borealis in the Northern Hemisphere And the Aurora Australis in the Southern Hemisphere

Only iron, steel,nickel and cobalt are magnetic. Summary of Magnetism Only 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

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