Magnetism_Concept_3
Magnetic Fields
Magnetic Fields
Earth's magnetic field
The Earth has a core of molten nickel and iron. It is thought that friction, caused by movement within the core, generates electrical pulses.This flow of electricity acts like a giant coil, turning the core into a giant magnet. NBThis has nothing to do with gravity: all planets produce a gravitational field, but only those with an iron core seem to produce a magnetic field. Although the Earth's magnetic field has been known about since ancient times, it has still not been adequately explained.
Magnetic poles
The Earth's geographical North Pole and its magnetic north pole are in slightly different places, less than 800km apart.The North and South Poles are the ends of the axis about which the Earth rotates.The magnetic north pole is in northern Canada and the magnetic south pole on the edge of Antarctica, near Australia. The magnetic north pole was first officially visited in the 1 860s —but if you were to visit that point now, you would be over 100km away from the current magnetic north pole.The magnetic poles are slowly moving, at a fairly constant rate.This is because the magnetism comes from the Earth's core, which is molten and is constantly flowing•
If you were to draw a diagram of the lines of force in the Earth's magnetic field (in the same way as in Figure 3 in concept 2), the lines at the magnetic poles would be vertical.
Magnetic compasses
Pieces of lodestone floating freely on water (for example, supported by a thin mat) or dangling on a string have been used to find directions for a very long time.The needle of a compass, which is a magnet, aligns itself with the Earth's magnetic field and points to magnetic north.The Earth's magnetic field is relatively weak in any particular location, and is easily disrupted by other magnetic fields.
Concentrations of magnetic materials (such as a metal-framed table or a school building) can lead to an inaccurate compass reading of magnetic north.The flow of electricity (which generates an electromagnetic field) nearby will also deflect a compass.
Testing the Earth's magnetic field
The strength of the Earth's magnetic field can be compared with the strength of a magnet by using a compass. Set up the compass in a place (such as the school playing field) where local magnetic disturbance is minimal, so that the compass reading is accurate. If you then bring the north-seeking pole of a magnet up to the north-seeking end of the compass needle, the needle will turn away to give an opposite reading. Check using the position of the Sun, which will always appear in the southern portion of the sky (in the northern hemisphere) during the middle of the day. (NB Children should not look directly at the Sun.) Slowly withdrawing the magnet will reduce the repulsive force until the compass is pointing to somewhere in between magnetic north and the pole of the magnet. At this distance, the magnet's field balances that of the Earth (in terms of their effect on the compass).
You can never be entirely sure that the compass is pointing true' north.The Earth's magnetic field is not perfect, and there are lots of local variations; but at least this activity demonstrates that the Earth has a magnetic field. Carrying out the above activity with the children would be an extension at KS2; it will be enough for the children just to read about the use of a compass, or for you to explain it to them.
The earth's magnetic field, with its link to th North and South Poles, is a key area of scientific and geographical study. While gfeography focuses on the uses of magnetic field, science examines its properties.e
Magnetic Compass - a free floating magnet which aligns itself with the Earth's magnetic field.
Magnetic North and magnetic South - the points on the earth's surface where the lines of force in the magnetic field are vertical.
The earth's magnetic north pole is moving at an average rate of nearly 2km per year.
Magnets have been used as an aid to navigation since before written records of travel began. It is known where in the world magnets were first used for this purpose, but it certainly made finding your way around when you can't look to the sky for direction possible.
A compass needle points to the North Pole. This statement shows an incomplete understanding which may lead to embedded misconceptions later. It is necessary to distinguish between the geographical North Pole and the magnetic north pole. Children should also be aware that a compass needle can be deflected by local magnetic influences.
Compass making (design and technology)
A bar magnet dangled on the end of a string might be expected to settle and align itself with the Earth's magnetic field, but may give inexact results: this field is quite weak, and a slight draft or the winding of the cord may affect the magnet's direction. Another option is to float the magnet on a polystyrene boat' or thin cork mat in a bowl of water.The boat will need to be quite small in relation to the bowl, or it will touch the side and affect the magnet's position.