Learners observe the pattern of the magnetic field around magnets through the use of iron and steel filings.
After completing this tutorial, you will be able to complete the following:
The Greeks discovered a mineral around the fifth century BC that could attract pieces of iron. The mineral was found in a region of Turkey called Magnesia, so the Greeks called this fascinating mineral magnetic. The mineral, an iron oxide, is now called magnetite. Because of the rock's chemistry and the Earth's magnetic field, a small amount of magnetite on Earth is found to be magnetized. The Middle English people called it lodestone, meaning "course stone" or "leading stone," because it was used in navigation. Recent research has revealed that only a variety of magnetite with a certain crystalline structure, a combination of magnetite and maghemite, has sufficient coercivity to be magnetized and become a permanent magnet.
A magnet is a material that produces a magnetic field, which exerts a force on other magnets and magnetic materials. Cobalt, iron, nickel, and some of their alloys are magnetic. In the atoms of most elements, the magnetic properties of their electrons cancel each other out. However, in the atoms of cobalt, iron, and nickel, these magnetic properties do not cancel each other out. Each atom of these elements has its own magnetic field and acts like a small magnet.
A permanent magnet is made from a material that stays magnetized; pure iron cannot be made into a permanent magnet, but steel can be. Materials that can be magnetized are called ferromagnetic and include cobalt, iron, nickel, some of their alloys, and some naturally occurring minerals, such as magnetite or lodestone. Some metals are attracted by magnets, but most are not. All magnets have a north and a south pole. These poles are where the magnetic force exerted by the magnet is the strongest. The lines of force are directional from north to south. A bar magnet has north and south poles at opposite ends. A magnet shaped like a horseshoe has a north pole on one end and a south pole on the other and these are in close proximity. A disc-shaped magnet has opposite poles on the top and bottom. Like poles are repelled by each other, and unlike poles are attracted to each other.
The Earth has its own magnetic field. Although scientists are unsure of the exact cause of the Earth's magnetic field, they believe it is associated with the Earth's core and call this the Dynamo Theory. The inner core of the Earth is made of a solid ball of iron and nickel and is surrounded by a layer of molten iron and nickel. Scientists believe that the Earth's magnetic field is mostly caused by electric currents in the liquid outer core. Convection of the molten iron of the outer core, along with the effect caused by planetary rotation, tends to organize these electric currents along the north-south polar axis, creating a magnetic field. As molten fluid flows across the already existing magnetic field, more electric currents are induced, which creates another magnetic field. When the magnetic field reinforces the original magnetic field, a dynamo is created, which sustains itself.
Imagine that a magnet exists within the center of the Earth and that its south magnetic pole tends to face geographical north, and its north magnetic pole tends to face geographical south. The south magnetic pole attracts the north pole of a magnet or compass and is currently located in northern Canada, about 1,500 km from the geographic north pole. The Earth's magnetic field shifts over time and has moved about 10-15 km per year over the last one hundred years. Scientists who study layers of magnetic rock indicate that Earth's magnetic poles have changed places over 150 times throughout its history.
The Earth's magnetic field is used for navigation. It seems that the Chinese were the first to use compasses, but reports vary regarding when this practice began. Chinese literature as early as the fourth century BC reported that lodestone attracted iron and that a "south pointer" could be carried with a person to prevent them from getting lost on their journeys. Chinese sailors were known to use the magnetic needle compass for navigation by the twelfth century.
|Approximate Time||20 Minutes|
|Type of Tutorial||Experiment|
|Key Vocabulary||chalk, copper, experiment|