For the recent a few centuries, understandinghow to use electricity and how to generate electric power has been consideredas the most important invention for the human history. Nowadays, there is noway that our human beings can live without electricity: from big machines likethe refrigerators, the air conditioners, the washing machines, to small deviceslike lamps and cellphones, almost every second in our daily life we need todeal with electric appliances and electronic devices. Although most people know how to useelectricity and understand its importance, many of us may not be familiar withthe twin brother of the electricity – the magnetism. Perhaps the understandingof the majority of people on magnetism is still on the level of refrigeratormagnets or compasses, I have to say that the interconnection betweenelectricity and magnetism is inseparable. From the largest scale of facilitiesthat is related to electricity like the generators in the power plant, to themuch smaller scale of devices like a headphone and a microphone, the magnetismplays a critical role in all those areas.First of all, I would like tointroduce some fundamentals and history about the relationship betweenelectricity and magnetism.

In the ancient time, people studied and consideredelectricity and magnetism as two separated subjects that were paralleled toeach other. However, in 1820, a Danish physicist called Hans Christian Oerstedoccasionally observed that a compass needle was deflected when got close to anelectric circuit that was switched on and off, and following by furtherresearch, he found and realized that was the first connection betweenelectricity and magnetism, and it is known for Oersted’s Law. Oersted’s Lawimplies that an electric current creates a magnetic field. In 1831, Englishscientist Michael Faraday published his study that indicated when part of theclosed circuit moves cutting the magnetic lines near a magnet, an inductingelectric current would be produce in the circuit, which is known as Faraday’slaw of induction. Faradays’ law of induction reveals the fact that usingmagnetism we can generate electric power. From that time, people realized that electricityand magnetism were tightly connecting to each other, and with the deeper anddeeper studying on them, our human beings were stepping into the age ofelectricity.

Nowadays, the electricity makes ourlives much better and more convenience. We can enjoy an ice cream by pluggingthe refrigerator into the wall; we can light up the night by plugging the lampsinto the wall; we can use all electric appliances by simply plugging them intothe wall. But have you even thought about where does the electricity on thewall come from? Okay, the answer is that the electricity on the wall comes fromthe generators in the power plant, and the electric generator is built based onFaraday’s law of induction. A generator in the power plant is a device thatconverts mechanical energy from a gas turbine or a steam turbine into electricpower for our daily usage on the principle of electromagnetic induction foundby Faraday.

As introduced before, electric current can be induced by moving apart of the closed circuit like a wire in a magnetic field that cutting itsmagnetic lines, and if we increase the intensity of the magnetic field,increase the length of the wire that cutting the magnetic lines, and increasethe speed of the movement, we can generate an enormous net electric potential.That is the basic idea how a generator is built and how it works, coilsspinning in a large magnet, and the electric current will flow in the coilsthat is distributed to every houses. I believe most of people have theirown cellphone today, and many of them are fancy smartphone that can do muchmore than a phone should do – making a phone call. Although it is hard toimagine that there are magnets in our cellphone since they usually are not ableto be attracted on the refrigerator, it is true that every cellphone hasmagnets in it, and they are the important parts that makes the speaker and themicrophone in the cellphone work. The speaker in the cellphone turns theelectric signal to the sound signal, and it has three major parts to finishthis job: a cone, a coil, and a magnet. The cone, or sometimes call the diaphragm,is acting like a drum skin that can make sound when vibrating.

The front partof the cone is connecting to the speaking hole in the front of the faceplate ofthe cellphone, and the rear part is connecting an iron coil, that just in thefront of a permanent magnet. The speaker employs the principle of Oersted’sLaw: when the speaker is in use, electrical currents will flow through the wiresto the coil, and the electrified coil will produce a magnetic field based onthe direction of the current. As the electric current in the coil that carries theinformation changes back and forth, the coil will either attract or repel the permanentmagnet, so that the moving coil will make the cone vibrating, and that is howthe speaker in a cellphone works. On the other hand, the microphone in acellphone has exactly the same physical structure as the speaker, but theprinciple of operation is reversed: it turns the sound signal to the electricsignal. When we are speaking to the microphone, the sound waves make the conevibrating, and the moving cone pushes the coil back and forth. As how Faraday’slaw of induction implies, the moving coil in a magnetic field produced by thepermanent magnet will generate electric current, and that is how the microphonein a cellphone turns the sound signal to the electric signal.After finishing my briefintroduction on the historical background and some daily examples showing howelectricity and magnetism interconnects with each other, I believe most ofpeople will have a better understanding on the importance of magnetism’sinterdependence with electricity. No matter from the small devices like thespeaker or the microphone in our cellphones, or from a large generator that cansupply electricity for the whole city, it is obvious that magnetism existswherever electricity exists, and that is why electricity and magnetism aretwins brothers.

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