
V ∞ I
Under this condition we characterize the electrical behavior of the body, wire, by its resistance R, which is defined by the following formula,
Figure (1): Simple resistive circuit

V = i R
Where V is the voltage difference in volts, between the two ends of the wire, i is current in amperes and R is a parameter called resistance in ohms.
Equation above is the well known as Ohm’s Law. The resistance of a conducting body can have any value between wide limits depending on the material type and geometry of the body. The resistance of a conducting body usually varies with temperature. Devices used in circuits to provide fixed resistance of known values are called resistors. Electrical energy is converted into heat when current flow through a resistor. Thus resistor is used as heaters elements. They are also used to control current and voltage in circuit. If the relation between the volt and current linear relation, for certain resistance, we call this resistance an ohmic resistance. Resistors are usually represented in the circuit diagram as
The Ohm’s Law is obey the relationship that is shown as the graph below.