Electric current – our irreplaceable assistant, but maybe a source of serious danger. The nobility what current consists in and as it is correct to use it without harm for himself and people around, it is necessary and it is useful. Precisely current is measured by special devices – ampermeters. It is very simple to use modern digital ampermeters.
In school textbooks by physics electric current call the directed movement of electric charges. However to compare current with a water consumption in a pipe, and tension – with its pressure, incorrectly. It will be also wrong to identify the movement of charges with movement of free electrons.
Speed of drift of free electrons in conductors is very small - about 10 mm / page. Electric current – distribution of the electromagnetic field in the conductor or in space.
In what current?
If on the conductor to give tension, that electric field in it will change. There will be kind of an expectation of the suitable train in the subway. Here, train approached, doors opened - it we closed a chain: inserted a plug into the socket, clicked the switch. People went, in the movement they emit energy. It can be used: to put, for example, a turnstile, and let twist.
That is in electric field there is an energy stock. If balance of the field is broken – the chain is closed, a certain door is open for charges – current will go. But that its energy turned into work or heat, current has to test a certain resistance. Carriers of charges (electrons, ions) "turnstile" (heater, the motor, a bulb) will not revolt, and they will regularly work for us. So, current – its ability to make some action, caused by an energy stock in the electromagnetic field. But that the ability turned into work or heat, it is necessary to put tension still: weak-willed will not scroll a hard turnstile even if ahead the way is free. 1 A currents at 1 V of tension will give work in 1 J and if it is made during 1 with, then power will turn out in 1 W. But at a zero tension the current of any force will not perform work – its force will be spent for nothing.
Current of very big force at almost total absence of tension is possible in superconductors.
As measure current
Current is measured by special devices – ampermeters. In household testers multimeters there is a mode of measurement of current too; on the switch it is designated by letters A (amperes) or mA (milliamperes; 1 mA = 1/1000 A). To measure current by the ordinary ampermeter or a tester, it needs to be included in a rupture of a wire. Now there are ampermeters allowing to measure current without breaking an electrical circuit. For this purpose or put the special sensor (Hall's sensor) to a wire, or cover a wire an ampermeter ring – current pincers. Magnetic action of current on which judge its force is measured in that and other case.
Action of current on the person
Action of current on the person depends on his look – constant or variable – time of influence and current. The most dangerous – current of the industrial frequency of 50/60 Hz, that, which in the socket. Its action on the person is defined, including influence time in 1 village.
The value of the industrial frequency of 50/60 Hz developed historically and is technically unprofitable. Before it became clear, the world power developed, and it is impossible to change frequency now.
Current with a force of 0.1 mA for the person is imperceptible. Current in 1 mA causes easy tingling. 3 mA give notable blow, and after – a fever and other unpleasant feelings; over time manifestation of different side effects is possible. 10 mA cause spasms, it is not releasing current. 100 mA are considered current deadly if the victim within 15 min. was not delivered to the intensive care unit. Current through the conductor depends on the enclosed tension as breakthrough of crowd to doors – from a pressure behind. This dependence is expressed by the known law of Ohm. Resistance of a human body can change over a wide range therefore for rules of electrical safety take the smallest of possible values – 1000 Ohms. Proceeding from it safe tension 12 V and less are considered. An effective measure of protection against defeat by a current is protective grounding. By analogy with the rushed crowd: widely open for it a spare entrance, and it freely passes there, without having trampled anybody.