Long ago certain rocks were found to attract iron. These rocks were the first magnets. Magnetism has been known about for centuries. Chinese and Greek mythology contain references to this "magical" property. According to the Encyclopedia Britanicia, the mineral magnetite - a magnetic oxide of iron - appears in Greek writings from as early as 800 B.C. This mineral, which even in the natural state has a strong attraction for iron, was mined in the Greek province of Magnesia, in Thessaly. Pliny the Elder, however, ascribes the name to its discover, the shepherd Magnes, "the nails of whose shoes and the tip of whose staff stuck fast in a magnetic field while he pastured his flocks."
Scientists think that the atoms of most materials act as tiny magnets, each with a north and south pole. The ends of the magnets are known to have different properties, and were given the the arbitrary names of north and south poles. If the atoms in a magnet or other object are arranged with their poles helter-skelter, then the attraction or repulsion of a north pole is cancelled by the opposite force of a nearby south pole. When this occurs, magnetic force is not noticed outside the object. However, if most of the atoms have their poles lined up, then the attraction or repulsion of all the north poles at one end are not cancelled out and the magnetic force is noticed. At the other end of the magnet, the forces exerted by the south poles of the atoms build up into the strong force of a south pole. The center of a magnet is weak because the force of every north pole is cancelled by the force of a nearby south pole.
Materials differ in the ease with which their atoms can be lined up. In non- magnetic materials, the atoms don't turn around and line up very easily. The magnetic field surrounding a strong magnet can temporarily magnetize objects made of iron, steel, nickel, or cobalt. When an iron nail is brought near the north pole of a magnet, the south poles of the atoms are pulled around to line up facing the north poles. The particles of a nail are lined up in one direction and the whole nail becomes a temporary magnet. But if the nail is taken away from the magnet, the particles revert back to their random distribution and the nail's magnetism disappears.
Warn students that magnets will break or lose their magnetism if dropped, hit together, or heated. Such actions cause the particles to rearrange themselves, decreasing the effectiveness of the magnet. To store a U-shaped magnet, place a piece of soft iron called a keeper, across the ends. Bar magnets and other shapes of magnets can be stored as they normally attract each other with opposite poles which are close or touching.
The first application of magnetism was the compass. Some writers believe the compass was in use in China as early as the 26th century B.C. Others believe that it was introduced to China in the 13th century A.D. and its invention was of Italian or Arab origin.
The most important properties of magnetism are connected with the relationship between magnetism and current electricity. The use of the magnet and its electrical counterpart, the electromagnet, is the foundation of much modern technology. While the characteristics and uses of the electromagnet will not be taught directly in the Utah State Core Curriculum until 5th grade, a study of magnetism can be a fun beginning point for introducing students to structured inquiry/discovery activities.
Students are fascinated by magnets and their seemingly magical properties. Each one student will want the opportunity to manipulate and explore the properties of different magnets, so many of these activities will be best organized in small groups or teams. A science learning center (where materials can be left on a table for students to explore) is an effective introduction or follow-up, if organization permits.
Students naturally want to explore and share their discoveries outside of the classroom with family and friends. While most magnets are fairly expensive, school supply, craft, and science outlets often sell small magnets for use on bulletin boards or refrigerator doors at a reasonable cost. If possible, provide one for each studnet to use at home and explain that the classroom set of magnets must remain in class for group activities.
Electric charge is both negative and positive. In the atom, electrons having a negative charge are outside the nucleus which contains protons having a positive charge. Electricity is a flow of negatively charged electrons.
While understanding the properties of magnets can help in the understanding of electricity, magnetic poles and electric charges are different things. They happen to obey similar rules for repelling and attracting, but they are different. To understand the difference, think of apples and oranges. They will be much the same, do the same thing taste and look like a fruit, but they are not the same; apples and oranges do not grow on the same tree. It is important to point out that magnetism and electricity are different.
Static electricity is a buildup of electric charge that does not move. Static electricity occurs when non conductors of electricity such as rubber, plastic, glass, amber, clothing, and hair gain or lose electrons. Static electricity is recognized by the attraction or repulsion on one object for another, such as hair raising to follow a brush.
Current electricity is electric charge in motion. For current electricity to occur, two things are needed: (1) a source for the electricity like a battery, motor, or a generator, and (2) electricity must flow along a pathway. A conductor makes the best pathway; while an insulator prevents the flow of electrons. Most conductors are made of metal. A bulb or an electric appliance may be part of the pathway. Electrons are returned to the battery or generator along the pathway making the electric circuit.
Another example of an electric current is a lightning bolt. When so much static charge builds up that the air can no longer insulate opposite charges, a large current in the form of a discharge occurs. This discharge allows opposite charges to recombine, forming neutral combinations and lowering the static charge. The sparks that occur when you touch metal after walking across carpet are the same occurrence in miniature.
There are many kinds of circuits. A closed circuit is a complete loop in the flow of electricity. A typical example of a closed circuit includes a battery - wire - bulb - wire - battery. If there is a break in the flow of electric charge, the circuit is said to be open. The principle of open and closed circuits is used in creating on/off switches for lights and appliances.
Circuits can be constructed in series or parallel. A series circuit occurs when the electricity leaves the source (battery), travels along the pathway (wire), through the bulb (receiver), and back along the pathway to the source. A series circuit can contain several lights but has only one continuous pathway. An example of this kind of circuit is found in Christmas tree lights where the entire string of lights goes out if one bulb is missing or not functioning.
In a parallel circuit, each bulb or receiver has its own pathway to the source so that it forms its own circuit. In a parallel circuit, Christmas tree lights do not go out if one light in the strand is not functioning.
Resistance is a quality of some materials that, when used as a pathway for electricity, allows the electricity to move but with difficulty. When electrons meet resistance, heat, and sometimes light, is produced. The light bulb has a filament of fine wire with great resistance, usually tungsten, which creates light. Toasters and irons create heat by using resistance.
An electric current has a magnetic field around it. This magnetic field is seen in the construction of an electromagnet, which is made by wrapping a wire, the pathway, into coils. Electromagnets are used in doorbells and telephones as well as large metal moving machines. The advantage of an electromagnet is that it can be controlled by turning on and off the electrical current.
Many scientists have contributed much to the development of electricity and the creation of the many devices which use electricity. Many words used in electricity are named for these scientists. Ampere gave his name to the unit used to measure current. The ampere is a measure of the amount of charge that flows past a point per second and is measured by an instrument called an ammeter. Resistance is measured by the ohm which bears the name of its discover. Ohm's law states that voltage is equal to the product of the current times the resistance. Voltage is the push needed to force electrons to move and is named for Volta. Electrical power is measured in watts or kilowatts, also named after the scientist, Watt.