Concept of electric current
Still, characterizing quantitative value of electric current, many use such terminology as, for example, small current, big current. Such assessment of current is absolutely unsuitable for its characteristic from the point of view of work which it can carry out. When we speak about work of current, we mean that its energy will be transformed to any other type of energy: warmly, light, chemical or mechanical energy. The more the flow of electrons, the is more considerable current and its work.
The word "current" has two values. It designates the phenomenon of the movement of electric charges in the conductor and also serves as assessment of amount of the electricity passing on the conductor.
Current (or current intensity) is evaluated quantity of the electrons passing on the conductor during 1 page. Its number is huge. Through filament of the burning bulb of the electric pocket small lamp, for example, every second there pass about 2000000000000000000 electrons. It is quite clear that it is inconvenient to characterize current by quantity of electrons as it should deal with very large numbers. The ampere is taken for unit of electric current (in abbreviated form write And). So it was called in honor of the French physicist and the mathematician A. Ampere (1775-1836) who studied laws of mechanical interaction of conductors with current and other electric phenomena. Current 1 A is current of such value at which through transverse section of the conductor for 1 with there pass 6250000000000000000 electrons. In mathematical expressions current is designated the Latin letter I or i (it is read and). For example, write: I 2 A or 0,5 A.
Along with ampere apply smaller units of current intensity: milliampere (write the mA), equal 0,001 A, and microampere (write the mk), the equal 0,000001 A, or 0,001 mA. Therefore, 1 A = 1000 mA or 1000000 mk. The devices serving for measurement of currents are called ampermeters, milliammeters, microampermeters. They are included in the electric circuit consistently with the consumer of current, i.e. in the rupture of the external circuit. On schemes these devices represent circles with appropriated to them by letters inside: And (ampermeter), the mA (milliammeter) and the mka (microampere), and nearby write RA that means the current measuring instrument.
The measuring device is expected current no more than some limit for this device. The device cannot be turned on in the chain in which the current exceeding this value, differently flows it can deteriorate.
The ampermeter (the milliammeter, the microampermeter) is turned on in the electric circuit consistently with the consumer of current.
You can have the question: how to evaluate alternating current which direction and size continuously change? Alternating current is usually evaluated on its operating value. This such value of current which corresponds to the direct current performing the same work. The operating alternating-current value is about 0,7 amplitude, i.e. maximum values.Top