Many confuse electric current with voltage. But it not the same. These terms though are interconnected with each other, but designate absolutely different physical quantities.
Instruction
1. Electric current call the process arising in the conductor at application of voltage to it. The intensity of this process called current depends on the enclosed tension and resistance of the conductor. The more tension is less than resistance, the current is stronger.
2. In metals the current arises thanks to movement of carriers of a charge - free electrons - between knots of a crystal lattice. In other firm conductors the leaping of electrons from one atom on another is the reason of current. In semiconductors both the electronic, and hole current is possible, and a hole is called not the particle, but the place of its absence at all. Hole current moves aside, opposite to the direction of the movement of electrons. There are semiconductors with electronic and hole conductivity, and, its type depends generally not on the substance, and on composition of impurity in it. In liquids and gases carriers of current are generally ions, in a vacuum - freely flying electrons.
3. In spite of the fact that the direction of current depends on that what particles of a charge transfer it, the following is considered its conditional direction: in the power supply - from minus to plus, beyond its limits - from plus to minus. This direction was accepted for conditional long before it became clear that electrons - the most widespread of current carriers - actually move in the opposite direction.
4. Electric current is measured in the amperes called so in honor of the French physicist André-Mari Ampere. The thousand share of ampere is called milliampere, million - microampere. Thousand amperes are called a kiloamper, one million amperes - megaampere.
5. The device for measurement of current is called the ampermeter. There are also milliamperemeters, microampermeters, etc. Mirror and electronic microampermeters are most sensitive. Current can is also measured in the contactless way on magnetic field by means of the device called klampmetry.
6. Excess of current through the conductor is capable to lead to its fusion, ignition of its isolation. Use the fuses and reusable automatic switches which are shortly called automatic machines to protection against such situations.
7. The current passing through a human body is felt at value in 1 milliampere, at 10 milliamperes becomes dangerous, at 50 milliamperes - can become deadly, at 100 milliamperes - almost always becomes that.
8. If loading has negative dynamic resistance, current through it should be limited. For this reason all gas-discharge lamps feed not directly, and through ballasts.