1, ancient human understanding of static electricity
About 2,500 years ago, the ancient Greek philosopher Thales (640-546 BC) (electrostatics is the oldest natural phenomenon in physics-the history of physics) discovered that amber rubbed with silk and flannel can attract light and small objects. Therefore, Thales became the first electrostatic experimenter in history. The word electricity comes from the Greek word ε λ ε κ ο ν (amber).
In the 3rd century AD, it was also recorded in Zhang Hua's "Natural History" of Jin Dynasty: "Today, people comb their hair and undress, some with the comb and some with the hiss." The flash and crackle of hair caused by friction and electrification are recorded here.
But until the16th century, there was no record of static electricity except the occasional discovery of elmo fire. Elmo fire is a luminous phenomenon, which occurs on or near the mast of a ship. There is a story of "divine fire" in the hands of water sailing in the Mediterranean for a long time. At the critical moment in shanghai dawn, they repeatedly found ominous flames on the mast tip. At first, the sailors thought it was the end. But when they escaped safely many times, fire became a source of comfort. Sailors named it "The Fire of Saint elmo" to symbolize the protection of their belief in Saint elmo.
2. The establishment of the basic theory of classical electrostatics.
Willian Gelbert (UK, 1540- 1603), the father of electricity, repeated Thales' experiment. He wants to know why amber, an ornament, has the characteristics of attracting light and small objects after rubbing. Do other jewels have similar properties? He experimented with other jewels and found that diamonds, opals and sapphires have the characteristics of attracting other light and small objects such as amber after rubbing. He later discovered that other objects have similar properties, such as amethyst, glass, black marble, sulfur, wax and so on. He noticed that although these substances can attract the east after friction, they do not have the property of pointing in the north-south direction like magnets. He called these substances charged by frictional energy "triboelectricity". An object that cannot be charged by friction is called an "uncharged object".
In order to further study the attraction of these objects, Gilbert also invented the first electroscope to test charged objects. This is a thin needle made of light wood or metal, and its center can rotate. When the rubbed amber approaches, the fine needle can rotate. He also found that when the weather is dry, these objects are easily attracted. Gilbert is called the father of electricity. Soon, otto von gehrig (1602- 1686, German) discovered the repulsion of electricity. If charged metal rods are close to metal fragments, they will attract each other and then repel each other.
1678 Glick made the first friction electric starter. He crushed and melted sulfur and poured it into an empty glass ball with a diameter of six inches. There's a stick in the middle, important official. After sulfur is cooled, the glass ball is crushed and made into sulfur ball. When the ball rotates rapidly and rubs the sulfur ball with cloth or directly by hand, it can produce great sparks. 1709, British scientist (Francis Hauksbee, 1666- 17 12) made an electrostatic generator similar to Guericke, which used a big wheel to drive a small wheel to make the small ball rotate faster. He calculated that the linear velocity of the ball reached 29 feet per second. When rubbing the ball with fur, he felt a breeze when he put his face close to the charged ball. After continuous improvement, this friction electrostatic starter played an important role in electrostatic experiments, and it was not replaced until19th century when W. Holtztr and A.Topler invented the induction starter respectively. He also invented the first electroscope. Hanging the bent straw on one end of the insulated metal rod, he found that when the charged body approached, the straw would repel and open. His other important discovery was that when two balls with a distance of 1 inch were put together and rubbed against one of them, both balls would glow, which he didn't understand at that time. This is actually electrostatic induction.
Stephen Gray (1666- 1736, English) discovered in 1720 that silk, dry wood and hair can be charged by friction. He found the difference between conductor and non-conductor when studying the transmission of amber attraction characteristics. He wiped an empty glass tube about one meter long. In order to keep the glass tube clean, he put a plug at one end of the glass tube. When he rubbed the glass tube, he found that the plug could also attract light and small objects. He thinks this attraction can be passed on. Since then, he has continued experiments to test this transmission ability of electricity. He drilled a small hole about an inch straight in an ivory ball, then inserted a small stick, and the other end of the stick was inserted into the plug of the glass tube. He found that the ball had the same attraction when rubbing against the glass tube. He replaced the stick with a fishing rod 18 feet long, and the experiment was successful. Later, he experimented with thread, and he found that the thread connected to the glass tube stopper can also transmit this property. Then he connected a three-foot hemp rope to the plug, and the ivory ball was still very attractive. To further test this property, he stood at the top of the house and found that ivory could still attract feathers even if he stood 34 feet high. He also found that the wet line spread farther than the main line. Since there are no higher cliffs or buildings near him, he wants to extend the line horizontally. He hung the wire on the beam of a house, and then the attraction stopped. He thinks the current has entered the beam. Glanville Wilt, a good friend of Gray's, suggested using silk as the suspension wire, because silk can prevent the loss of electric energy. After adopting Wilt's suggestion, Gray increased the wire to 100 m, but the wire could no longer bear such a load. At this time, he changed the silk thread into metal thread to increase the strength, but he found that the experiment was invalid. Finally, he switched to thicker silk thread and the experiment was carried out again, as shown in Figure 6. From these experiments, Gray thinks that some materials such as iron and copper are conductors, while others such as silk are insulators.
Charles Du Fei (1698- 1739, French) 1733 found that insulated metals can also be charged by friction after repeated Gray's experiments. He thinks that any substance can be charged as long as it is insulated, so Gilbert is wrong to divide objects into "friction charged objects" and "non-friction charged objects". He experimented with gold foil and found that charging gold foil with a triboelectric glass rod would repel another gold foil with the same charge and attract gold foil charged with a triboelectrically charged hard resin. He thinks there are two kinds of electricity, one is virus electricity (now we call it positive electricity) and the other is resin electricity (now it is called negative electricity). It occurred to him that objects with the same charge repel each other and objects with different charges attract each other. But he did not define the positive and negative polarities of these two kinds of electricity.
Benjamin Franklin (1706- 1790) thought that there were two kinds of charges, namely, positive charge and negative charge. One of his famous experiments was that two people stood on a platform made of wax, and the third person stood on the ground. After rubbing the glass rod with cloth, one person stands on the insulating platform and charges with the glass rod, while the other person stands on the insulating platform and charges with cloth. If the fingers of these two people touch, they will feel an electric shock. If either of them touches a person standing on the ground and then touches the other person with his finger, the electric shock will be weaker. 1747, he thinks that the polished glass rod is positively charged and the resin is negatively charged. Although this is a great step, science may reverse Franklin's choice in the future. If so, electrons may be defined as positively charged rather than negatively charged. Of course, the direction of positive current is the direction of electron movement, not the opposite direction. Franklin thought that static electricity was not caused by friction "friction charged substance", but by the transfer of "electric fluid". Although this concept is not completely correct, the actual process is basically consistent with the later findings.
Ewald (1700- 1746, German) filled a glass bottle of 1745 with half a bottle of water, put a stopper on it, and then put a nail through the stopper until the nail just touched the water. Then, he connected one end of the nail to the electrostatic motor, so that electric energy was transmitted to the water through the nail. He found that this bottle can store electricity. When stored to a certain extent, it can attract small objects or generate sparks. Later, he replaced water with other liquids such as mercury and alcohol, which could produce bigger sparks. This bottle that can store electricity is the first capacitor. Professor Pieter von Musschenbroek of Leiden University (1672- 17 1, Dutch) repeated Ewald's experiment. He separated the inside and outside of the bottle with metal foil, and inserted the metal wire from the stopper of the bottle mouth until it touched the metal foil in the bottle, thus inventing the Leiden bottle.
The invention of Leiden bottle provided conditions for the further study of electricity and played an important role in the dissemination of electrical knowledge. Jeau Antoine Nollet (French) once did one of the most spectacular demonstration experiments at that time. In front of the members of Louis XV's royal family in Paris Cathedral, he made 700 monks form a 900-foot-long team hand in hand, and one end of the team touched the outside of the charged Leyden bottle. When the other end touched the other end of the Leyden bottle, 700 monks jumped up because of electric shock. The invention of Leyden bottle provided a new tool for Franklin's great discovery. Franklin connected a wire to the inner wall and the outer wall of the Leyden bottle, separated the wires by a certain distance, put them on the table, hung a plug with silk thread, and let it swing back and forth between the two wires and touch them respectively until the Leyden bottle was not charged, which proved that there were positive and negative charges on the inner wall and the outer wall of the Leyden bottle.