Ohm's Law: Voltage, Current and Resistance Explained

Objectives

• Study the effects of Ohm's law on linear conductors and electric current.
• Study the functional relationship between the voltage applied to a resistive element and the electric current passing through it.

Background

Ohm's law, electric potential definition, electrical current, electrical conductivity, resistance and resistivity.

Introduction

Ohm's Law describes the relationship between voltage and current in conducting elements. This relationship is a characteristic function of the conductive material and determines whether the behavior between voltage and current is linear or nonlinear. The slope of the V–I line corresponds to the resistance.

Conductor Behavior and V–I Characteristics

For a conductor where the current–voltage relationship is constant: V / I = R (constant), the conductor is said to be linear (ohmic). The voltage/current graph is a straight line through the origin.

In a conductor in which the ratio V / I is not constant, we say that the conductor is non-ohmic (nonlinear) and the graph is a characteristic curve. In other words, the resistance depends on the voltage(s) applied across the material.

Electric Field

An electric field is a characteristic of space due to the presence of electric charges.

Electric Current

Electric current is the flow of charge per unit time through a material. It is caused by the movement of electrons (or charge carriers) inside the material. Current is measured in amperes and is denoted by the symbol A. Because it is a movement of charges, an electric current produces a magnetic field.

Electric Conductivity

Electrical conductivity is the ability of a body to allow passage of electrical current through it. It is a material property that represents the ease with which electrons (and holes, in the case of semiconductors) can move through the material. Conductivity varies with temperature and is one of the most important characteristics of materials.

Electrical Resistivity

Electrical resistivity is the degree of difficulty encountered by electrons in motion. It is denoted by the lowercase Greek letter rho (ρ) and is measured in ohm-meters (Ω·m). It is sometimes expressed in Ω·mm²/m.