There are several basic measurement parameters electric current. The most important are considered current and voltage. Current is the movement of electrons in a conductor, voltage- this is what sets them (electrons) in motion. However, for a complete description of all parameters, we will also talk about such characteristics as power, resistance and frequency, which we will talk about when we give the definition of alternating current.

Current strength- measured physical quantity, which is equal to the ratio of the amount of charge passing through certain time through the conductor (more precisely, its cross section), to the value of the specified time interval. As we know, current is measured in Amps (A).

Electric voltage The ratio of the work of current to charge in a certain section of the circuit is called. The current charge is measured in Coulomb (C), and work is measured in Joules (J). Thus, the voltage can be measured as follows: 1J / 1C. The resulting value will be equal to 1 Volt (V) - the basic unit in which voltage is measured.

current power called the work done by the particles of electric current against electrical resistance. We see the results of this work in the released thermal energy. Therefore, to put it simply, the power of an electric current is the amount of heat generated per unit of time. Measure power in watts (W).

Electrical resistance. At one time, the German scientist Georg Simon Ohm noticed that devices give out different current strengths when using different electrical circuits. Thus it was proved that different conductors have different electrical resistance. The formula for calculating resistance is simple. We mark the resistance itself with the letter R, L will denote the length of the conductor, and S is the cross-sectional area. In this case, the resistance is calculated by the formula R=L/S. Resistance is measured in ohms.

Resistance determines how much a material resists the passage of electric current. The greater the resistance, the more voltage is needed to provide the desired current.

electrical voltage affects how carefully the conductors should be insulated. The higher the voltage, the greater the likelihood of insulation breakdown. Higher voltages require more reliable insulation. Higher voltage bare wires should be placed further apart, away from other electrically conductive materials, and away from earth.

Higher voltage is more dangerous. But one should not think that low voltage is completely safe. Damage to health from electric shock depends on the strength of the current that has passed through the body and its trajectory. And the current strength already depends on the voltage and resistance. The resistance of the human body is determined by the resistance of the skin. Internal organs and environments are excellent conductors of current. Skin resistance can vary tenfold depending on emotional state, physical activity, humidity and a dozen other factors. There have been cases of fatal 12 volt electric shocks.. The strength of the electric current determines which wires to use. The higher the current, the thicker the wire needed.

The power of electric current is measured using a wattmeter. One of the terminals of the current winding must be connected to one of the terminals of the voltage winding. These terminals in the instrument are connected to terminals marked with an asterisk. Therefore, before turning on the wattmeter and the circuit, first, using an insulated wire of short length, connect the clamps marked with an asterisk. Power in DC circuits, as well as in AC circuits in the absence of capacitors and electrical receivers with windings (for example, motors) can also be measured indirectly: using an ammeter and a voltmeter. According to the readings of the ammeter and voltmeter, the power is calculated using the formula known from physics.

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Measuring instruments can be classified according to two criteria: design; metrological purpose

CLASSIFICATION OF MEASURING INSTRUMENTS ... A measuring instrument is a technical instrument or a complex of them ... Other distinguishing features of measuring instruments are, firstly, the ability to store or reproduce a unit ...

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POWER ELECTRICAL

a value characterizing the rate of change (conversion, scattering, transmission, etc.) electric. energy. In chains post. current M. e. is equal to the product of voltage and current. In AC circuits current distinguish between instantaneous, active, reactive and full M. e. Instant M. e. is equal to the product of the instantaneous values ​​of voltage and current. Active M. e. - the average value of the instantaneous AC power over the period. current; characterizes cf. electromagnet conversion rate. energy into other types of energy (thermal, mechanical, etc.). In single-phase alternating circuits. current (sinusoidal) active M. e.

P = U I cos f, for a three-phase current P \u003d root of 3UI cos f (U and I are the effective values ​​​​of voltage and current, f is the phase shift between current and voltage). Active M. e. can be expressed in terms of current I or electric. voltage U and active resistance circuit r or its conductivity G according to the formula: P \u003d I 2 r \u003d U 2 G. In any electric. chains active M. e. is equal to the sum of active M. e. otd. chain sections. Unit active M. e. - W (see Watt). Reactive M. e. characterizes the rate of energy accumulation in capacitors and inductors, as well as the exchange of energy between dep. sections of the circuit and, in particular, the generator and receiver. In sinusoid circuits, reactive current M. e. section O \u003d \u003d U * sinf. Unit reactive M. e. - var. Full M. e. characterizes M. e., given to the circuit by a source of alternating. current. For sinusoid circuits, the current is full M. e. S= UI= root of (P 2 + Q 2). Unit complete M. e. - volt-ampere (V-A).

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