SIMPLE PHENOMENA OF MAGNETISM

Specific outcomes

• Describe properties of magnets
• Distinguish the magnetic properties of iron and steel.
• Demonstrate induced magnetism.
• Demonstrate the plotting of magnetic field lines.
• Demonstrate the making of a magnet
• Demonstrate the way to destroy a magnet
• Explain the domain theory of magnetism
• Explain the use of magnetic screening and magnetic keepers.
• Describe the uses of magnets.

CONTENT

Magnetism is a force exerted by magnetic objects without touching each other. A magnetic object is surrounded by a magnetic field, a region in space where a magnet or object made of magnetic material will experience a non-contact force. Electrons inside any object have magnetic fields associated with them. The way the electrons’ magnetic fields line up with each other explains magnetic fields in ferromagnetic materials (e.g. iron), magnetisation, permanent magnets and polarity of magnets. These concepts are explored with descriptions, diagrams and investigations.

Properties of Magnetism

Magnets have a pair of opposite poles, north and south. Like poles of a magnet repel; unlike poles attract. It is not possible to isolate north and south poles – even if you split a magnet, you only produce two new magnets. The magnetic field line around a bar magnet can be visualised using iron filing s and compass needles. Learners need to be reminded that the field is three dimensional, although illustrations depict the fields in 2D. To show the shape, size and direction of the magnetic fields different arrangements of bar magnets are investigated and illustrated.

Magnetic Fields

The pattern of the Earth’s magnetic field is as if there is an imaginary bar magnet inside the Earth. Since a magnetic compass needle (a north pole) is attracted to the south pole of a magnet, and magnetic field lines always point out from north to south, the earth’s pole which is geographically North is magnetically actually a south pole. The Earth has two north poles and two south poles: geographic poles and magnetic poles.

The geographic North Pole, which is the point through which the earth’s rotation axis goes, is about 11,5 away from the direction of the Magnetic North Pole (which is where a compass will point). Learners are made aware of the importance of the earth’s magnetic field acting as a shield to stop electrically charged particles emitted by the sun from hitting the earth and us. Charged particles can damage and cause interference with telecommunications (such as cell phones).

Solar wind is the stream of charged particles (mainly protons and electrons) coming from the sun. These particles spiral in the earth’s magnetic field towards the poles. If they collide with particles in the earth’s atmosphere they sometimes cause red or green lights, or a glow in the sky which is called the aurora, seen at the north and south pole.