Units of measure of Ampere and Volts belong to two different physical quantities of current and tension. However, despite this, they are in close functional interrelation.
Current
Current defines quantity of the charge passing through the cross section of the conductor per unit of time. That is the formula determining the physical quantity of current expresses the relation of quantity of a charge by the time of its passing to chains. Thus, current actually speaks about the speed of course of a charge in an electrical circuit. If with current passes through the section of the conductor in one second the charge equal to one Pendant, then the corresponding current equals to one Ampere. So current unit is defined.
Unit of voltage
Physical quantity of tension is determined by degree of an invertirovannost of charges on opposite poles of an element of a chain. In other words, tension on any site of a chain of subjects is more, than more difference in charges on the ends of the site. For example, tension on plates of the condenser is equal to the work of electric field strength between facings and distances between them. Thus, the tension of the field (the it is stronger) is higher, the tension is more.
Current is proportional to tension
So, tension depends at most electric field. But, as we know, the electric field strength also creates current in a chain because the loaded parts are affected by Pendant force, forcing them to move. Respectively, the Pendant force is higher, the more there will be a speed of charges, so and current. Thus, both the current, and tension are directly proportional to electric field strength. However not all charges proceeding in the conductor due to electric field will reach its end. Some of them face atoms of substance of the conductor, and their mobility falls. And the possibility of the conductor to carry electric current depends on a substance sort and also its geometrical parameters. What the electron will longer move to chains, that high probability of the fact that it will encounter an ion of substance of the conductor. To characterize extent of attenuation of mobility of electrons on the site of a chain, resistance size is used. It is the proportionality coefficient connecting the current and tension. This regularity found the reflection in the law of Ohm which allows to find current size if the value of the given tension and also resistance of this site of a chain is known.