Most of us are familiar with magnets. They are used in everyday life. Very simple applications are such as the magnets used for sticking decorations on fridges. Magnets are also used for lifting small objects such as pins and clips. The tips of many tools such as screwdrivers are magnetised so as to lift the nuts and screws. Importantly, magnets are used for knowing the direction. This is because a freely suspended magnet shows the north and south direction of the Earth. This forms the basis of the magnetic compass. A graduated compass can be used to locate the Qiblah, the direction of Makkah Mukarramah required for offering Salaat (Namaz or Prayers).
The study of the magnets dates back to ancient times. The ancients were fascinated by their ability to attract iron and show direction. In modern understanding, we say that every magnet has two poles: “north seeking pole” and a “south seeking pole” which we simply call the north-pole and the south-pole respectively. The opposite-poles attract and the like-poles repel. When a magnet is broken, we obtain a pair of magnets. It is not possible to separate the poles. They always occur as a pair within a single magnet. The Earth behaves as if it has a huge bar magnet inside it. The Earth’s magnetic field is a mystery, which is an active field of research. Geological studies point to the fact that the direction of the Earth’s magnetic field reverses after few million years.
In the 19th century two discoveries were made: (1) a wire carrying electric current behaves like a magnet; and (2) a moving magnet induces current in a coil of wire near it. The first discovery led to the invention of very powerful electromagnets, with controlled properties by changing the current. The second discovery gave birth to the dynamo and the transformer. These discoveries revolutionised the technological applications of magnetism and electricity. It will be difficult to imagine a life without electricity and magnetism. Many applications of magnetism include motors, loudspeakers, variety of measuring instruments. Magnetic memories are used in making videos, compact discs, flash memories and computer storage devices. High magnetic fields are used in medical diagnostics from high resolution images obtained using techniques such as the MRI (magnetic resonance imaging). Such techniques have certain advantages over traditional X-Rays.
FLOATING MAGNETS
Like-poles of two magnets repel. This property can be used to float magnets. This is easily achieved using two-ring magnets. Ring magnets are cylindrical magnets with a hole in the centre. The diameter is usually much larger than the height of the magnets. The ring-magnets are present in speakers and microwave ovens. A wooden dowel (rod or pole) or a pencil is vertically attached to a wooden block by a screw. The first ring-magnet is placed over the wooden dowel. The second magnet is brought close to the first magnet to feel the magnetic forces and decide which of the two poles repel. After identifying the repelling pole the second magnet is placed over the dowel in such a way that the like-poles face each other. This makes the second magnet float. In a similar manner, the third ring-magnet is also placed over the dowel.
The procedure can be repeated to place several more ring-magnets on the dowel. The force of gravity pulls the magnets down and closer to each other. The force of repulsion between the like-poles overcomes the force of gravity and makes the magnets float. The distance between the first and the second magnet is the least, followed by the second and the third, followed by the third and the fourth, and so on. The first magnet has to bear the weight of all the magnets; hence the distance is the least. The assembly of magnets on the dowel behaves very much like a spring.
If the magnets are pushed down, they resist, just like a spring. Care needs to be taken while bringing the unlike-poles of the magnets together. The force is strong enough to cause injury and damage. One can also attach a pan on the topmost magnet on the dowel and make a weighing device. The numbers can be marked on a scale attached to the dowel.
Magnets have numerous applications in our life. The force of repulsion between the like-poles can be used to levitate the magnets. It would be an interesting exercise to study the pattern of the increasing gaps between the ring-magnets on the dowel.
[HAJIRA KHAN is studying at Indian School, Salalah, Oman &SAMEEN AHMED KHAN is on the Engineering Department, Salalah College of Technology (SCOT), Salalah, Oman. [email protected]]