We can’t do without electricity every day, and we also know that household electricity comes from power plants. But how do power plants generate electricity? Who was the first to discover this principle? To understand this, we must first start with a character – Faraday.
1. Electromagnetic induction phenomenon
After the Danish physicist Oster discovered the magnetic effect of electric current, the British physicist Faraday thought: Since electric current can generate a magnetic field, can the magnetic field generate an electric current? Because in Faraday’s time, people used zinc, copper and zinc for electricitysaltwaterThe voltaic battery made is troublesome to make, the voltage is small, and the electricity emitted is not suitable for ordinary people. ButnatureThe magnet resources of the world are very rich, and if magnets are used to generate electricity, then electricity can enter thousands of households.
Faraday conducted painstaking experiments for this ideal, and his initial idea was to place a magnet in a solenoid in anticipation of generating an electric current in the circuit, but it was never successful. Finally, in 1831, Faraday’s experiment made a breakthrough, and he discovered that current is generated in the circuit only when the magnet is inserted or pulled out of the solenoid.
We can use modern methods to equate Faraday’s experiment to the above situation: when a solenoid is connected to an ammeter and a magnet is inserted into the solenoid, the ammeter will produce an indicator. Also, the faster you insert it, the more deflection the ammeter needle will be. Similarly, during the process of the magnet pulling out the solenoid, the ammeter needle is deflected, only in the opposite direction. However, if the magnet remains stationary in the solenoid, there is no current generated in the circuit.
Faraday finally understood: only inmotionand change process to generate electric current. Faraday summarized his findings into five cases, which were applied to modern generators: Cutting a conductor of a magnetic induction wire in a magnetic field can generate an electric current.
For example, we connect a wire to the ammeter and make the wire move to the right, so that the wire cuts the magnetic induction wire like a knife, and an electric current will appear in the circuit. And we can use the right-hand rule to judge the direction of the current: if the magnetic induction wire passes through the palm of the right hand and the thumb points in the direction of the wire movement, then the direction of the four fingers of the right hand is the direction of the generated current.
According to this principle, Faraday made early generators, while the British Chancellor of the Exchequer was skeptical of the use of generators. He asked Faraday: Your invention is interesting, but what is the use of it?
Faraday said: Your Excellency, maybe you will be able to collect taxes on it soon.
Sure enough, electricity has become us nowlifeAn essential part, who doesn’t pay for electricity?
2. DC and AC
Early generators produced direct current. The so-called direct current is the current that does not change the direction of the current. Nowadays, our household electricity is alternating current, the so-called alternating current, which is the current that changes periodically in the direction.
Specifically, there is a wire in the two-hole socket called the “neutral wire”, and the neutral wire voltage is the same as that of the earth, so touching the neutral wire will not give you an electric shock. The other wire is called the “live wire”, and the voltage of the live wire is higher than the earth for a while and lower than the earth for a while. Because the current flows from high voltage to low voltage, the current sometimes flows from the live wire through the electrical appliance, and then flows back to the neutral wire, and sometimes flows from the neutral wire through the electrical appliance and then back to the fire wire, each cycle is 1/50s, called 50Hz alternating current. The biggest advantage of AC power over DC power is that it is very easy to change the voltage, so that high voltage transmission can be carried out to reduce losses.
So, how is this alternating current generated?
Alternating current can be generated by a coil turning in a magnetic field. For example, in the picture: when the coil rotates, the right wire moves upwards, and according to the right-hand rule, the generated alternating current flows from c to d; The left wire moves downward, and the generated alternating current flows from A to B, so the current flow in the whole circuit is in the direction of C-D-A-B. The outer end of the coil is connected to an external circuit by two brushes, so that the current can flow through the bulb from top to bottom through the brushes.
After half a cycle, the coil rotates half a circle, and the AB and CD switch positions, and the current direction changes to B-A-D-C, so that the current flows through the bulb from bottom to top. Thus, alternating current is formed. If the coil rotates at a constant speed, a sinusoidal alternating current is formed.
In other words, as long as the coil can rotate relative to the magnet, an electric current can be generated. In modern generators, it is not the coil that rotates, but the magnet, called the “rotor”. The coil is immovable and is called a “stator”. At the same time, due to the needs of the engineer, there are three sets of generator coils, and any two sets of coils are sandwiched at a 60-degree angle.
In this way, as the magnet rotates at a uniform speed in the coil, three sinusoidal alternating currents are generated in each of the three sets of coils, each 1/3 cycle behind the previous one.
These three AC currents will have a common neutral wire (neutral wire) and a different live wire (output wire). When supplying power, if we connect one live wire and a neutral wire to the electrical appliance, it is 220V for household electricity, and if we connect two live wires to the electrical appliance, it becomes 380V for industrial electricity.
So, how can we make a coil or magnet turn? It depends on the type of generator. Hydroelectric generators rely on the impact of water to make the turbine rotate, wind turbines rely on fan blades to rotate the generator, and thermal generators rely on combustion to heat water vapor to drive the turbine. This process requires the consumption of external energy. In short, a generator is a machine that converts other forms of energy into electrical energy.
After the generator was invented, all kinds of electrical appliances sprung up, and mankind entered the electrical age.
3. Those who have never gone to schoolsciencegreat master
Let’s talk about Faraday again – the man who brought humanity into the age of electronics. Faraday was born into a family of blacksmiths, and due to his family’s poverty, he dropped out of school after only two years of elementary school and became an apprentice to a bookseller. However, this job exposed him to a large number of books and various documents that ordinary people could not access, and he was deeply fascinated by science.
With the help of an old patron in the bookstore, 20-year-old Faraday had the honor of listening to a lecture by chemist David. He also wrote a letter to David and mailed the compiled speech transcripts, expressing his willingness to dedicate himself to science.
David looked at Faraday’s resume and said to him: “Young man, I want to tell you that science is very hard and not very rewarding. ”
Faraday replied: “I think science itself is a reward. ”
David was moved, and Faraday finally became an assistant in David’s laboratory, and his scientific dream became a reality from David’s laboratory. Later, Faraday made amazing achievements in physics and chemistry and became the greatest scientist of his time.
Faraday was also a man of high moral character. Because of his early experience, he attached great importance to the training of young scholars and encouraged a group of scientific giants like Maxwell. He refused to be knighted for himself, twice refused to become president of the Royal Society of Sciences, and expressed his unwillingness to be buried in Westminster Abbey, the resting place of Newton and others. Therefore, people buried him in other cemeteries, but erected a monument to him next to Newton’s tombstone in Westminster Abbey.
By the way, his introductory mentor David was also a famous chemist, and it is believed that David’s greatest contribution was the discovery of Faraday……
