Once students understand the basic principles of magnetism phenomena, they create simple electric motors using permanent magnets and electromagnets to investigate the factors that affect how fast the motor spins.
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Trains that Float on Air
The world’s fastest train is in Shanghai, a city in China. This train is called the Shanghai Maglev. It reaches speeds of 431 kilometers per hour (268 miles per hour). It can travel 30 kilometers (18.6 miles) in seven minutes and 20 seconds.
The Shanghai Maglev is able to reach such speeds because it uses giant magnets to float over the tracks. (Maglev is short for magnetic levitation.) Floating above the tracks offers the trains a significant advantage. There is very little friction to slow the trains down. Engineers in the United States are discussing using maglev trains to connect the East and West Coasts.
Maglev trains work because they use a kind of magnet called an electromagnet. Electromagnets are tightly wound coils of wire that produce a magnetic field when electricity passes through the wire. They are useful in various technologies because the magnet can be turned off and on. This is different from permanent magnets, which stay magnetized without electricity.
Electromagnets Use Electricity
Electromagnets become magnetized when electricity moves through the wire. Electricity is the flow of electrons through a conductor. Electricity is all around us. It is found in our bodies as electrical impulses and in the sky during storms as lightning. It also powers much of our modern world, turning on lights and powering motors, cell phones, and many other technologies.
Electricity happens because of the structure of matter. Remember that all matter is made of tiny particles called atoms. Atoms are made up of even smaller particles, including protons, neutrons, and electrons. Protons and neutrons are found in the nucleus, and electrons orbit the nucleus at different distances called shells. Protons have a positive charge (+), and electrons have a negative charge (-).
Interactions of Charged Particles
Charged particles change the space around them. They produce an electric field that can exert a force on other charged particles within the field. Similar to magnets, charged particles either attract or repel one another. Particles that have an opposite charge attract one another within their electric field, while particles with the same charge repel one another within their electric field.
Electrons are kept in orbit in their shells because the positive charges of the protons in the nucleus attract the negatively charged electrons. The strength of the field weakens with distance. Because of this, electrons in shells closest to the nucleus are tightly bound. Electrons in the outermost shell are much more loosely bound. When a force is applied, electrons in the outer shells can be pushed from one atom to another. Once that first electron has been pushed away from its atom, it moves to another atom. This movement of electrons causes electrons to all move in the same direction as one another. It is the movement of these electrons that creates electricity.
Moving Electrons
Electrons can move more easily through some materials than others. Electric conductors are materials that allow electrons to pass through them easily. Metals such as copper and aluminum are electric conductors because they have electrons that are loosely held, and therefore can easily be pushed from their shells by an outside force.
Electric insulators are materials that do not allow electrons to pass through easily because electrons do not easily separate from their atoms. Rubber and plastic are both good electric insulators. This is why electrical cords are covered in rubber or plastic. The electricity cannot travel through the rubber or plastic and is forced to follow the path on the aluminum or copper wires.
Some materials are semiconductors, which means they can sometimes act as a conductor, depending on what other molecules are around.
Electromagnets are Part of a Circuit
Because electromagnets are made with electricity, they can be demagnetized when the electricity is turned off. This is possible because electromagnets form a circuit. A circuit is the circular path that electrons travel in a negative to positive direction.
All circuits have the same basic parts. All circuits have an energy source such as a battery. The battery has stored chemical energy that converts to electrical energy, which is the energy of electrically charged particles. The battery’s energy provides the input of force that pushes the electrons in the conductive material through the circuit.
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