Cavendish was born in England in 173 1. He spent his whole life in laboratories and libraries, and spent his life in the Cavendish of Chemistry and Thermology.

And electricity. However, due to his contempt for honor, he paid little attention to publishing experimental results and gaining priority in discovery, which led to many of his achievements not being published. It was not until the middle of19th century that people found some extremely precious materials from his manuscripts, which proved that he had made great contributions to the development of science. Cavendish's most acclaimed scientific contribution is that he first studied the distribution of charges on conductors and explained the law of electric power interaction with similar experiments in 177 1 year. In his report to the Royal Society in 1777, he said: "The attraction and repulsion of electricity are probably inversely proportional to the square of the distance between charges. If so, almost all the excess electricity in the object is concentrated near the surface of the object. The electricity is tightly pressed together and the rest of the object is in a neutral state. " At the same time, he also studied the capacity of the capacitor; A group of capacitors with known capacity are manufactured and the capacitance of various instrument samples is measured. The dielectric constants of different substances are predicted, the dielectric constants of several substances are measured, and the concept of "potential" is put forward preliminarily. Cavendish devoted his whole life to scientific research and engaged in experimental research for 50 years. He was withdrawn and rarely contacted with the outside world. Cavendish's main contributions are as follows: 178 1 year produces hydrogen for the first time, and its properties are studied. Experiments show that it produces water after burning. However, it is a great pity that he once mistook the discovered hydrogen for phlogiston. 1785, cavendish discovered the existence of inert gas by introducing electric sparks into the air. He has done many successful experimental studies in chemistry, heat, electricity and gravity, but rarely published them. A century later, Maxwell sorted out his experimental papers and published a book entitled "Dear Henry cavendish's Electrical Research" in 1879. Only then did people know that Cavendish had done many electrical experiments. Maxwell said: "These papers prove that Cavendish foresaw almost all the great facts in electricity, which became famous in the scientific community through Coulomb and the works of French philosophers." Long before Coulomb, Cavendish had studied the charge distribution on the conductor. 1777, he reported to the Royal Society: "The attraction and repulsion of electricity are probably inversely proportional to the square of the distance between charges. If so, almost all the excess electricity in the object is accumulated near the surface of the object, and the electricity is tightly pressed together, and the rest of the object is in a neutral state. " He also proved the force between charges through experiments. He proved through experiments that before Faraday, the capacitance of a capacitor depended on the substance between two plates. He first established the concept of potential, pointing out that the potential at both ends of a conductor is directly proportional to the current passing through it (Ohm's law is established in 1827). It was impossible to measure the current intensity at that time. It is said that he bravely used his body as a measuring instrument to estimate the current intensity by feeling the electric vibration from his fingers to his arms. One of Cavendish's great contributions is that he completed the torsion balance experiment for measuring gravity in 1789, which was later called the Cavendish experiment. He improved the torsion balance designed by the British mechanic Michel (John Lin Kewei, 1724 ~ 1793), added a small plane mirror to its suspension system, and used a telescope for remote operation and measurement outdoors, thus preventing air disturbance (there was no vacuum equipment at that time). He hung a 6-foot-long wooden pole with 39-inch silver-plated copper wire, fixed a small shot with a diameter of 2 inches at each end of the wooden pole, attracted them with two large fixed shot with a diameter of 12 inch, measured the swing period caused by gravity between the shots, and calculated the gravity of the two shots, and then calculated the mass and density of the earth from the calculated gravity. He calculated that the density of the earth is 5.48 1 times that of water (the modern value of the density of the earth is 5.5 17g/cm3), from which the value of the gravitational constant g can be calculated as 6.754×10n m? /kg？ The first four digits of the modern value are 6.672. The conception, design and operation of this experiment are exquisite. British physicist J.H. Poynting once commented on this experiment: "It initiated a new era of weak force measurement". Cavendish published a paper on artificial air in 1766, and won the Copley Medal of the Royal Society. He made pure oxygen and determined the contents of oxygen and nitrogen in the air, which proved that water is not an element but a compound. He is called "Newton in chemistry". Cavendish worked in his own laboratory all his life and was called "the richest scholar and the most learned millionaire". Cavendish died in March 18 10.

Cavendish torsion balance experiment

1789, cavendish, a British physicist, successfully measured the value of the constant of universal gravitation with a torsion balance, which proved the correctness of the law of universal gravitation. Cavendish's thinking to solve the problem is to change the small change that is not easy to observe into the obvious change that is easy to observe, and then calculate the small change according to the relationship between the obvious change and the small change [1].

Experimental principle

Cavendish put a big iron ball and a small iron ball at both ends of the torsion balance. A steel wire with good toughness is tied to the bracket in the middle of the torsion scale, and there is a small mirror on the steel wire. When a mirror is illuminated with a laser, the laser will be reflected far away, and the point where the laser is at this time will be marked. Use two iron balls with the same mass to attract two iron balls on the torsion balance at the same time. Because of gravity. The torsion balance has a slight deviation. However, the apogee of the laser reflection has moved a great distance. He used this to calculate the constant g in the formula of universal gravitation. The ingenuity of this experiment lies in amplifying the effect of weak force. Especially, the utilization gravitational constant of light reflection is g = 6.67 *10-11.

Second, the main achievements

Achievements in the chemical field

In about 1784, cavendish studied the composition of air and found that in ordinary air, nitrogen accounts for four fifths and oxygen accounts for one fifth. He determined the composition of water and proved that water is not an element but a compound. He also found nitric acid.

Achievements in the field of physics

Cavendish rarely published physics papers before his death. It was not until Maxwell reviewed and published his manuscript that people realized that he had made many important discoveries in electricity. He found that the acting force between a pair of charges is inversely proportional to the square of the distance between them, which is part of Coulomb's law later deduced by Coulomb. He proposed that there is "electricity" around every charged body, which is very close to the electric field theory; Cavendish proved that the capacitance of a capacitor is related to the substance inserted into the plate. The concept of electric potential was first put forward by Cavendish and played an important role in the development of electrostatic theory. He also suggested that the potential on a conductor is proportional to the current passing through it. Cavendish has research in thermal theory, thermometry, meteorology and geomagnetism. When he finished his last experiment, he was nearly 70 years old. In physics, his main achievement is to verify Newton's law of universal gravitation through the torsion balance experiment, and to determine the gravitational constant and the average density of the earth. Newton was a scientist who measured the gravitational constant after he discovered the law of universal gravitation.

Calculate the density of the earth

Cavendish measured the density of the earth by looking for constants in Newton's law of universal gravitation, and then calculated the density of the earth. His guiding ideology is extremely simple, using two big shot puts to get them close to two small balls. The mutual attraction between the balls is measured from the torsion angle of the line from which the balls are suspended. According to the law of universal gravitation, the constant g can be found. According to cavendish's many experiments, the average density of the earth is 5.48 1 times that of water (the current value is 5.5 17, and the error is about 0.65253%), and the gravitational constant (the gravitational constant G he measured is (6.754 0.04 1) × 65438) is determined. /kg？ This value is the same as the modern value (6.6732 0.001) ×10n m? /kg？ , almost, calculated the mass of the earth. Known as the first person on earth. Cavendish's experiment to verify the law of gravity used his own "torsion balance" as a tool, which was later called the famous "Cavendish Experiment".