﻿ Voltage

# Voltage: general information

The volt is taken for unit of voltage, the electromotive force (EMF) (in honor of the Italian physicist A. Volt). In formulas tension is designated the Latin letter U (it is read "at"), and the unit of voltage - the letter B. For example, write: U = 4,5 B; U = 220 V. Edinitsa the volt characterizes tension on the ends of the conductor, the site of the electric circuit or terminals. Voltage of 1 V is the such electrical quantity which in the conductor with a resistance of 1 Ohm creates the current equal 1 A.

Scheme of connection of the voltmeter.

The battery of 3336 L intended for the flat pocket electric lamp as you already know consists of three elements connected consistently. On the label of the battery it is possible to read that its tension of 4,5 V. Znachit, tension of each of elements of the battery 1,5 of V. Napryazheniye of the Krone battery of 9 V, and tension of electric lighting network can be 127 or 220 Century.

Tension is measured by the voltmeter, connecting the device the clips of the same name to terminals or parallel to the site of the chain, the resistor or other loading on which it is necessary to measure tension operating on it. On schemes the voltmeter is designated the Latin letter V.

The voltmeter is connected parallel to loading or the current source, feeding the electric circuit. Apply to assessment of tension also larger unit - kilovolt (write kV), the corresponding 1000 V and also smaller units: millivolt (write mV), equal 0,001 B, and microvolt (write мкВ), equal 0,001 mV. This tension measures respectively by kilovoltmeters, millivoltmeters and microvoltmeters. Such devices as voltmeters, connect parallel to current sources or sites of chains on which it is necessary to measure tension.

Scheme of electric field intensity.

Let's find out now in what the difference of the concepts "tension" and "electromotive force". The electromotive force call tension operating between terminals until the external chain loading, for example the bulb of incandescence or the resistor is connected to it. As soon as the external circuit is connected and in it there will be current, tension between terminals will become less.

So, for example, the new, not being even in the use galvanic cell has EMF not less than 1,5 Century. At connection of loading to it tension on its poles becomes equal about 1,3-1,4 century. In process of expenditure of energy of the element its tension gradually decreases by the power supply of the external circuit. The element is considered discharged and, therefore, unusable for further application when tension decreases up to 0,7 Century. Though if to disconnect the external circuit, its EMF will be more than this tension.

And how evaluate alternating voltage? When speak about alternating voltage, for example about tension of electric lighting network, mean its operating value being approximately, as well as the operating alternating-current value, 0,7 amplitude values of tension.