Develop a fundamental understanding of physics, as a foundation to applying theoretical physics in any world situations, from engineering and environmental management to rural industries and health sciences
Physics involves studying the physical world around us; the things we can touch and the forces and energies that affect those things. It underpins our knowledge of so many other things we do, and industries we work in. Without physics we would not have television, computers, motor cars or airplanes. A knowledge of physics allows us to build bigger bridges and buildings than ever before, and know that they are solid and not likely to collapse. Physics allows us to light our cities, heat and cool our homes, refrigerate our food and mass produce our clothing and household goods. It underpins all of this and so much more.
This course gives you the broad based foundation needed to work with and learn more about most aspects of physics.
Magnets come in different shapes and sizes today, and most of us have already probably played around with a magnet or two before. We explained in the previous lesson that all matter contains electric charges, and that it is possible for an object to either have an excess of electrons (in which case the object will be negatively charged) or a deficit of electrons (which means that the object will be positively charged).
If you push two magnets against each other, you will notice that they may either attract or repel each other depending on the arrangement of their poles. By changing the position of one of the magnets with respect to the other, those magnets will sometimes attract each other and other times repel each other. As you already know, 2 similar charges would repel each other, whereas 2 different charges will attract each other – i.e. 2 electrons will repel, 2 protons will repel, but an electron and a proton would attract each other. We refer to those 2 types of forces as “attractive force” and “repellent force”.
We are all familiar with the effects of magnets where a magnet can exert a force on another material without any apparent means. This is due to magnetism which can either be due to the spin of electrons within an atom or due to electrons flowing in an electric current. When electric currents and magnetism are combined, they generate a powerful force which can be used for specific and useful devices.
Magnetic Forces
All magnets produce a force that will affect all other magnets. The force is referred to as the ‘magnetic field’. The magnetic field occupies the space around a magnet. It quickly dissipates with increased distance away from the magnet. When a magnet is place within iron filing, the filings quickly organise themselves along the magnetic field lines revealing the pattern of the magnetic field lines.
The magnetic field lines are different from electric field lines, this is because of the dipole nature of magnets and the monopole nature of electric fields.
Lines of magnetic force are usually marked with an arrow. This arrow indicated the direction that a free north pole would move. The lines do not denote anything actually moving along the line, just the direction a ‘free’ north pole would take.
The lines curve around from the magnetic north pole to the magnetic south pole.
Magnetic fields are measured by a unit called a Tesla, a smaller measurement is a Gauss. One Tesla is equal to 10,000 Gauss. A Tesla is derived by Newtons per Ampere meter (where a Newton is a measure of force named after Sir Isaac Newton. One Newton (N) =1 kb.m/s2.
Ferromagnetism
Materials that are highly magnetic are referred to as ferromagnetic. Some naturally occurring elements that are ferromagnetic at room temperature include iron ore, cobalt, nickel. Other magnetic materials include composites such as ferrite and rare-earth (lanthanoid series of elements). At low temperatures two other elements are magnetic these are: Gadolinium and Dysprosium.
Creating Magnets
In un-magnetised iron the molecules are ‘unaligned’. Molecules arrange themselves into closed clusters due to the molecular North Pole being attracted to its South Pole neighbour. An un-magnetised piece of iron such as this would show no outward force of magnetism.
The process of magnetising iron or steel for example involves arranging the molecules in a regionalised alignment or ‘domain’. This does not create new magnetism, it merely reorganises the molecules to allow the already existing magnetism to be realised.
Iron can be considered ‘soft’ or ‘hard’. Soft iron means that it can be magnetised and quickly de-magnetised. Hard iron retains the magnetism permanently, however when such magnets are heated or struck with force the domains tend to lose their domain.
Example of the Practical Application of Magnetism
A very simple electric motor makes use of the interaction between magnetic fields. Any conductor with a current placed into a magnetic field is going to have forces operating on it. This is known as a motor effect. A very simple motor uses this by placing a coil that is free to rotate within a magnetic field, when a current carrying wire is made into a loop the forces on either side will be in opposite directions. This creates a turning force or torque for mechanical rotation,
