The Wonders of electromagnetism
vol.1 When did coils and electromagnets first appear?
This articles republished the past articles have been reorganized and rewritten. It includes the past technologies and products information not currently handled by TDK.
Many objects that we use in our daily lives, such as TV sets, radios, computers, copiers and other office equipment, mobile phones and smartphones, portable music players and more are intricately related to electricity and magnetism. But, the list does not stop there. Trains and automobiles, medical devices, industrial equipment, satellites and rockets, they all would be impossible without harnessing the science of electromagnetics. The more technology advances, the more these devices tend to be like black boxes to the user. They work their magic, but we don't really know or understand how.
However, isn't it a pity that we do not get to appreciate the inventions and the genius that went into building these black boxes? This series of articles will attempt to remedy the situation by introducing some of the principles and ideas at work here. The topic could be described as exploring the wonders of electromagnetics. If reading these articles rekindles your interest in the natural sciences, all the better...
Wireless IC cards make use of electromagnetic induction for wireless communication
First, meet the two mascot characters who will accompany us on our journey of discovery, throughout the entire series of articles. The guy with the rather large head crowned by a large question mark is "Magmag." He is big on asking questions, always wondering about the whys and wherefores. His buddy is a little chap sporting a coil-shaped antenna. Called "Curly", he is brimming with curiosity and quick to catch information. As can easily be seen, these two characters are representations of a magnet and a coil. They get into all sorts of adventures. Let's join them on a journey exploring the wonders of electromagnetics.
When a magnet is moved rapidly back and forth near a coil, a current will start to flow in the coil. This phenomenon is called electromagnetic induction and should be familiar from experiments often done in science class at school. Electromagnetic induction is the most basic and important "performance" that Magmag and Curly can put on for us. It is the principle that makes possible both the electric motor and the generator.
Mobile phones and smartphones are becoming ever more clever, and they even can function as electronic money similar to wireless IC cards these days. Currently electronic money is still divided into various different systems, but efforts to create an international standard that will allow use anywhere are under way. Wireless IC cards make use of electromagnetic induction for wireless communication. Both the card and the reader/writer unit incorporate coils that interact via a magnetic link. The magnetic energy sent from the reader/writer is used to drive an IC chip integrated in the card, allowing the card to function and perform read/write operations without requiring a battery. This is possible because coils not only can generate a magnetic field, they also can pick it up and store it.
Exploring electromagnetism-it all began with Oersted's experiment
As we get underway on this journey of discovery, let us take a look at where Magmag and Curly came from. The phenomenon of electromagnetic induction was discovered by Faraday in 1831, but Oersted's famous experiment performed some ten years earlier, in July of 1820, is usually considered as the actual start of the study of electromagnetism. When Oersted ran a current through a conductor during an experiment using a Voltaic cell, he noticed that a magnetic needle that happened to be near the conductor twitched slightly. (According to some accounts, this was first noticed by a student or an assistant of Oersted's.)
Oersted's report of the magnetic effect caused by a current had an enormous impact on the scientific world and triggered many follow-up experiments. The idea of shaping the conductor into a coil (namely Curly's roots) probably was hit upon by experimenters in various locations independently, but in scientific history, the name of Poggendorff is usually associated with it. He placed the magnetic needle within the coil and also verified that the more windings the coil had, the larger the deflection of the needle would be.
Soon after, Gay-Lussac who is mostly known for his study of gases, discovered that a current in a conductor can turn a steel needle into a magnet without direct contact. Inserting a core made of steel iron into a coil and passing a current through the coil turned the core into a permanent magnet. The person who devised the magnetization method still in use today was Arago whose experimental setup is known as Arago's disk or Arago's wheel.
Following in Curly's footsteps, Magmag's ancestor saw the light of day in the scientific world of 19th century Europe. Of course, natural magnets were known already in the BC era, and the method of rubbing natural magnets on iron to create man-made magnets had been employed since ancient times. But, the idea of using electricity in a coil only came along in the 19th century, after actual experiments had been made possible by the discovery of the Voltaic pile and Voltaic cell in 1800.
The "right-handed screw rule" makes Ampere's law easy to understand
After Oersted discovered the magnetic effect of a current, the study of magnetics also advanced rapidly. For example, when a current is passed through a conductor routed perpendicular through a piece of heavy paper, iron powder scattered on the paper will become neatly arranged in a concentric pattern.
This phenomenon is similar to what happens when scattering iron powder around a magnet. Under the influence of Oersted's findings, many scientists performed such experiments, and it was established that current not only can produce a magnetic field but that the properties of that magnetic field are the same as those of a natural magnet.
If we consider a conductor with a flowing current as a magnet, it is likely that two such conductors should behave in a way similar to two magnets, capable of attracting and repelling each other. To prove that this is so, Ampere constructed moveable coils with a rectangular conductor shape and performed a series of experiments under strictly controlled conditions. He found that when the current flows in the same direction in both conductors, the conductors attract each other, while current flowing in the opposite direction causes repulsion.
As a skilled mathematician, Ampere was able to express the magnetic field created by the current as a mathematical formula. This became the foundation for a new discipline referred to by Ampere as "electrodynamics." The direction of the lines of magnetic force with regard to the direction of the current can be easily visualized by thinking of driving a right-handed screw into a material. This right-handed screw rule is a simplified representation of Ampere's law that defines the behavior in mathematical terms.
A coil through which a current is flowing behaves like a bar magnet, but which of the coil ends becomes the N pole and which the S pole depends on the coil's winding direction and the direction of the current. This may sound familiar, as the topic often comes up as an exam question or in a physics quiz. As shown in the illustration, there are various ways of memorizing the principle involved. The most useful one may be method 3 since it closely follows the underlying principle. All you need to remember is the fact that the magnetic force lines of a magnet exit at the N pole and return to the S pole, and the fact that the magnetic force lines of a conductor are right-handed with regard to the direction in which the current is flowing.