Principle
The solenoid is energized to produce a magnetic field such as that of a magnet bar. The circle in the figure for the cross-section of the wire, the point represents the current out of the screen, the fork represents the inflow of the screen; with an arrow in an elliptical circle is a magnetic line of force. When the direct current through the conductor will produce a magnetic field, and through the conductor made into a solenoid (Solenoid) will produce a magnetic field similar to a bar magnet. By adding a magnetic substance to the center of the solenoid, the magnetic substance is magnetized and the magnetic field is strengthened. Generally speaking, the magnetic field strength generated by the solenoid is related to the size of the DC current, the number of coils and the magnetic material in the center, and in the design of the solenoid, we will pay attention to the distribution of the coils and the selection of the iron conductive material, and use the size of the DC current to control the magnetic field strength. However, the resistance of the coil material limits the size of the magnetic field that an electromagnet can generate, but with the discovery and application of superconductors there will be opportunities to break through the existing limitations.
History
Sturgeon's electromagnet. In 1825 A.D., Englishman William Sturgeon (1783-1850) invented the electromagnet by wrapping a metal wire carrying an electric current around an insulated rod.
American physicist Joseph Henry (1797-1878), upon learning of this, was able to suck up a one-ton block of iron by wrapping dense coils around a soft iron core and energizing it with a battery that did not draw much current.
Making
Simple homemade electromagnet:
Needs enameled wire, iron nails for its body; battery or power supply to supply current.
Precautions:
To scrape the paint off the end of the enameled wire, or burn it with fire.
To wind the enameled wire in the same direction.
To tie a knot at the end of the enameled wire.
Properties
Electromagnets and permanent magnets have the strongest magnetic force at the ends.
The magnitude of the magnetic force of an electromagnet can be changed.
The direction of an electromagnet can be changed.
The magnetic force of an electromagnet can be controlled.
In 1822, French physicists Arago and Lussac discovered that when an electric current passes through a winding in which there is a piece of iron, it magnetizes the iron in the winding. This is actually the first discovery of the principle of electromagnet. 1823, Sturgeon also did a similar experiment: he is not a magnet on a U-shaped iron bar around 18 turns of bare copper wire, when the copper wire and voltaic batteries connected to the copper coils around the U-shaped iron bar on the copper coil that produces a dense magnetic field, which makes the U-type iron bar into a piece of "electromagnet! ". This electromagnet on the magnetic energy than the permanent magnet can put more times, it can absorb than it is 20 times heavier than the iron, and when the power supply is cut off, the U-shaped iron bar on what iron can not be absorbed, and become an ordinary iron bar. Sturgeon's invention of electromagnet, so that people see the bright prospects for the conversion of electrical energy into magnetic energy, this invention soon spread in the United Kingdom, the United States and some coastal countries in Western Europe. In 1829, the American electrologist Henry Sturgeon electromagnet device made some innovations, insulated wire instead of bare copper wire, so do not have to worry about being too close to the copper wire and short circuit. As the wires have an insulating layer, they can be tightly wound together in a circle, because the denser the coil, the stronger the magnetic field generated, which greatly improves the ability to convert electrical energy into magnetic energy. By 1831, Henry had tried out a newer electromagnet, and although it was not very large, it was able to suck up a 1-ton block of iron. The invention of the electromagnet also led to a significant increase in the power of the dynamo.