When the electrical field is increasing, the force acting on the electric charges is growing and, as a result, their movement is speeding.

In the conductors, such as copper or aluminium, direct proportionality between the current and the voltage exists. This proportionality was discovered by the German physicist, Ohm, which is why Ohm's law is known as such.

The current through a conductor between two points is directly proportional to the voltage drop across the two points.

This can be expressed mathematically as follows:

The constant R express the difficulty offered by a conductor in allowing a current to flow through it, and is known as electrical resistor.

For most metal conductors, the voltage drop applied between their ends is the linear function of the current that flows, which is properly in accordance with Ohm's law, and in such cases, these are known as linear or Ohmic conductors. The graphic representation of V-I is known as the conductor characteristic. Here we are assuming that conductors are linear. We should keep in mind the fact that there are many conductors in Nature for which Ohm's law does not work.

Voltage: Voltage is electric potential energy per unit charge, measured in joules per coulomb (Volts), e.g. 220 V.

Resistor: Resistor describes how a material can conduct electricity. Resistor is measured in Ohms (Ω), e.g. 25 Ω.

Check this link that shows the relationship between these 3 magnitudes:

http://www.online-learning.com/consulting/media/ohm/content/index.html [EN]