In this section dealing with the l7th and early 18th centuries the objective is now to begin formalizing the discussion a bit. Students should learn that Gilbert advocated the term electricity and a more scientific method, while also seeing that the idea of the earth as a magnet was also first postulated. In fact the earth is like a huge magnet.
According to Greek myths a young shepherd boy named Magnes discovered magnetism. While walking in the hills the nails in his sandals stuck to a rock. The name magnet was given to honor the young boy. Magnetite or lodestone. Again there are many books with demonstrations that you may want to try but I offer three.
Activities:
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1. What does earth's magnetic field look like? To do this demonstration you need a bar magnet, some iron filings, a couple of sheets of stiff white paper, and a marker, a copy of an outline of the earth and its continents. The bar magnet should be able to fit within the earth's outline. You may need to reduce or expand the diagram. After you have the drawing complete put the bar magnet under it. Then begin to lightly dust the map with the iron filings. You should gradually see the filings arrange themselves to mimic the magnetic field of the earth.
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2. Can we separate the Poles of a magnet? This experiment helps to point up a difference between static electricity and magnetism. Electricity can run in one direction and is gone. The magnetic attraction never leaves the field around its pole. It may bend or twist but it the field remains. No matter what we try we cannot separate the two poles. To try this demonstration you need a bar magnet, wire cutters, a large steel paper clip and a compass. You first need to unbend the clip and magnetize it by stroking it stroking it from the middle to the end about 50 times. Then turn the clip and repeat with the other end. You can test to make sure you have two poles by using the compass to verify this. Then you need to cut the clip in half. If you check the two pieces out with the compass you will see that each piece now has a north and south pole. You can keep cutting each piece again in half but you will continually get a new magnet. Cutting it in two does not separate the two poles. As you cut you will also notice that the magnet gets progressively weaker.
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3. How do the magnetic fields of two magnets affect each other? In doing this demonstration you will need 2 bar magnets, iron filings, and a sheet of stiff paper. If you dip the north pole of one magnet and the south pole of the other magnet into the filings and then bring them a short distance apart you will see that they seem to share the filings between them showing that the magnetic field is strong there. If you then take both north poles and dip them into the filings and bring them near you will see that the filings will retreat to the sides of the magnet showing how the like poles repel each other.
While scientists continued to study magnets no specific progress was made until William Gilbert (1544-1603) came along. Gilbert lived in Shakespearean England and was a doctor. At the time, many doctors were interested in magnetism. Since magnetism had certain effects on objects there was speculation that it might have healing potential for the human body.
Gilbert found that many objects besides amber could attract light objects. In order to gauge the ability of objects to attract, Gilbert invented the versorium. Versorium means, "turn around" in Latin. What the invention did was exactly that it turned toward or away from the object held near it. A long rod of any solid material even wood was suspended from a string. The rod would be rubbed vigorously and then the object would be held nearby. Gilbert made many other discoveries. He found that it was not heat that was given off by rubbing the rod that made amber attract light things but the friction. Gilbert is also credited with making up the word "electricity." If something placed near his versorium was not attracted it was a "nonelectric." If the object was attracted it was called "electric." Gilbert was the first to distinguish between magnetism and electricity. He also believed that the earth was a huge rotating magnet. This did not go over well with Gilbert's peers, many of whom believed that the earth was the center of the universe and stood immobile while the sun and planets rotated around it.
It is important to remember that up until this time most so called scientific experimentation consisted of mainly observation with little or no controlled experimentation. Gilbert brought this kind of discipline to the work he did. He set up experiments to prove his theories. It is important for students to understand the importance of the scientific method in solving scientific problems.
Students need to see that it was over two thousand years before any significant knowledge about electricity and magnetism was made. Gilbert's versorium is an interesting model to build with students and is quite simple. You will need a glass or plastic rod and then a length of thread. It should be tied around the rod so it can be suspended from a table so the rod can move freely. The rod then needs to be rubbed with a cloth until it gets warm. This is the most important part. After this is done the rod has to hang until it stops moving. Then bring a piece of paper near the rod and it will reach toward the rod. You can try other objects. If you tie a plastic ball point pen to a string and rub it with wool or some furry material then put it near the rod it will turn around and around. This proves again that like charges repel.
Stephen Gray (1695-1736) He was an Englishman who discovered that certain objects would carry an electric charge while others will not. He also figured out how to make an electrical charge (make electricity move). Objects that let an electrical charge pass are "conductors," while those that will not let a charge pass are insulators or nonconductors. Gray transmitted an electrical charge from a glass tube to an iron rod by using a wire. He was one of the first to use a wire as an electrical conductor.
What Gray did was clarify some ideas about static and current electricity. Up until now we have only static electricity because the charges positive or negative build up on an object or person and are not released till a conductor in many cases a piece of metal appears. Thus in walking across the rug we pick up a certain charge but we can't make the charge do anything unless it comes in contact with that conductor usually a doorknob and then we get that tiny shock and often see a spark of light. Now electricity is not held in an object but can be released. This ability to release the current would make electricity usable in the future.
Charles Du Fay a Frenchman (1698-1739) read some of the works of William Gilbert and Stephen Gray. He demonstrated that all objects could be electrified if they were heated and then rubbed with a cloth or fur. Even a conductor could be electrified if it were insulated. Du Fay is credited with identifying the two kinds of electricity, static and current. Static electricity is created by friction when certain objects are rubbed together. Current electricity is when electrons move through a conductor.