A device with an iron core inside and a current flowing in the coil to make it have the same magnetism as a magnet is called an electromagnet, and it is usually made into a strip or hoof shape. Electromagnets are mainly composed of coils, iron cores and armatures, and are generally made of soft magnetic materials. The iron core is generally static, and the coil is always mounted on the iron core. The spring is also mounted on the armature of the electromagnet of the switchgear. When the coil is energized, the iron core and armature are magnetized into two magnets with opposite polarities, and electromagnetic attraction is generated between them. When the suction force is greater than the reaction force of the spring, the armature begins to move towards the iron core; When the current in the coil is less than a certain value or the power supply is interrupted, the electromagnetic attraction is less than the reaction force of the spring, and the armature will return to the original release position under the action of the reaction force.
Electromagnet is an electrical appliance that uses electromagnetic attraction generated by current-carrying iron core coil to control mechanical devices to complete expected actions. It is an electromagnetic element that converts electrical energy into mechanical energy. Electromagnet has many advantages: the magnetism of electromagnet can be controlled by on-off current; The magnitude of magnetic force can be controlled by the intensity of current or the number of turns of coil. Electromagnets are widely used in daily life. Electromagnet is an application of current magnetic effect (electromagnetism), which is closely related to life, such as electromagnetic relay, electromagnetic crane and maglev train.
1822, French physicists arago and Roussac found that the iron blocks in the winding can be magnetized when current passes through the winding with iron blocks. This is actually the first discovery of the principle of electromagnet. 1823, sturgeon did a similar experiment: he wound 18 turns of bare copper wire on a U-shaped iron bar that was not a magnetic bar. When the copper wire is connected to the photovoltaic cell, the copper coil wound on the U-shaped iron bar generates a dense magnetic field, thus turning the U-shaped iron bar into an "electromagnet". The magnetic energy on this electromagnet is magnified many times than that of a permanent magnet, and it can attract an iron block 20 times heavier than it. When the power supply is cut off, the U-shaped iron bar can't absorb any iron and becomes an ordinary iron bar.
Sturgeon invented the electromagnet, which made people see the bright future of converting electric energy into magnetic energy. This invention soon spread in Britain, the United States and some coastal countries in western Europe.
1829, American electrician Henry made some innovations on the sturgeon electromagnet device. Insulated wires replace bare copper wires, so there is no need to worry about being short-circuited by copper wires. Because of the insulating layer, the wires can be tightly wound together. The denser the coils, the stronger the magnetic field, which greatly improves the ability of converting electric energy into magnetic energy. By 183 1, Henry has developed a newer electromagnet. Although it is small, it can absorb 1 ton of iron.
Electromagnets are widely used in modern society, such as electric fans, vacuum cleaners, electric bells, hair dryers, water pumps, washing machines, juicers, mixers, refrigerators, air conditioners, lawn mowers and so on. , are using the principle of electromagnet.
Bell, motor, telephone, etc. They all use electromagnets to produce actions.
The structure of electric bell is as follows, mainly including several designs: ① electromagnet; ② Spring leaf.
When the circuit is connected to the power supply, the electromagnet is energized to attract the reed. When the reed moves towards the magnet, the hammer strikes the bell to make a sound, and at the same time, the moving piece is in contact with the static piece.
When the circuit is in an open state, the electromagnet loses its magnetism, the reed is not attractive, and it will automatically bounce back to its original position under the action of elastic force, so that the moving piece is out of contact with the static piece, and the current flows to the bulb again through the electromagnet, forming a loop. The electromagnet began to work again, attracting the reed, and the hammer struck the clock again.
The bell kept ringing over and over again.
Audio tapes can record sounds, and computer hard disks can record data. These effects are achieved by using electromagnets of magnetic heads to change the properties of magnetic substances on magnetic tapes and disks.
The appearance of tape recorders can be traced back to 1877 when Edison, a great American inventor, invented the phonograph. Edison converted sound waves into vibrations of metal needles and recorded them on tin foil. Recording is achieved by using tin foil and metal needle. 1896, polson, a young Danish electrical engineer, converted sound waves into current and then into magnetic force to realize magnetic recording, and obtained a patent in 1898. But the real popularity of tape recorders came after the invention of magnetic tape. 1935, German scientist Frayema invented the magnetic tape and coated the acetate fiber tape with iron oxide, which officially replaced the steel wire. 1962 cassette recorder invented by Philips in the Netherlands.
Speakers use electromagnets to convert current into sound.
Sound box is also called "sound box". It is a very common electroacoustic transducer, which converts sound electrical signals into sound. The sound produced by the loudspeaker is an alternating magnetic field generated by a coil with an alternating signal, which attracts and repels the disc, causing the vibration of the diaphragm and the paper basin, and then spreads the sound through the air medium.
Speakers use both electromagnets and permanent magnets. Suppose you play the C key now (the frequency is 256 Hz, that is, it vibrates 256 times per second), and the record player will output 256 Hz alternating current. In other words, the direction of the current will change 256 times in one second. Every time the current changes direction, the direction of the magnetic field generated by the coil on the electromagnet will also change. As we all know, the magnetic force is "like attracts like, opposite attracts like". The magnetic pole of the coil constantly changes, attracting and repelling the permanent magnet for a while, resulting in 256 vibrations per second. The coil is connected to the membrane. When the membrane vibrates with the coil, it will push the surrounding air. Isn't vibrating air sound? This is how the loudspeaker works.
Electromagnets can not only convert electricity into magnetic force, but also convert magnetic force into electricity. On the same iron core, two groups of coils are used as two electromagnets, one of which inputs alternating current (electricity that changes the direction of current), and the other electromagnet has voltage output at both ends. The output voltage is related to the number of coils. The more coils, the higher the voltage. Using this principle, various transformers can be made to increase or decrease the voltage.
Transformer is a common electrical equipment, which can be used to convert a certain value of AC voltage into another value of the same frequency AC voltage, and can also change the value of AC, change the impedance or change the phase.
The power plant wants to transmit the power with P=3UIcosφ to the power-consuming areas. When p and cosφ are fixed, if the voltage is higher, the current in the transmission line will be smaller, so the loss of the transmission line can be reduced and conductive materials can be saved. Therefore, it is the most economical to use high voltage for long-distance transmission. At present, the highest voltage of AC transmission in China has reached 1000 kV. No matter the safe operation or manufacturing cost of the generator, it is not allowed to directly generate such a high voltage. The generator output voltage is generally 3.15kV, 6.3kV,10.5kV,15.75kV, etc. Therefore, before long-distance transmission, it is necessary to use a step-up transformer to increase the voltage. After the electric energy is delivered to the power-consuming areas, in order to meet the voltage requirements of electrical equipment, it is necessary to reduce the voltage to the voltage required by various electrical equipment through transformers at all levels.