Ohmic and Non-ohmic conductors are the two types of conductors based on their voltage-current characteristics. In this article let us learn about what are ohmic and non-ohmic conductors with examples and differences.
What are Conductors?
A material that allows electric charges or electricity to flow through them is called a conductor. The flow of electric current in these materials is due to free electrons. The free electrons are the electrons that are not permanently attached to an atom and can freely move throughout the material structure when external energy is applied. The movement of free electrons is responsible for the flow of electric current.
The current flowing through a conductor depends on the applied voltage and the resistance. Depending upon the relation between voltage and current, electrical conductors can be classified as either ohmic or non-ohmic. Using Ohm's law we can tell whether a conductor is a ohmic or non-ohmic.
Ohm’s Law :
Ohm’s Law states the relationship between current, resistance, and voltage. It states that the current flowing through the conductor is directly proportional to the voltage across the conductor.
In the above equation, R is the proportionality constant known as the resistance of the conductor. Resistance measures the opposition a conductor offers to the flow of electric current. It is measured in Ohms and denoted by the symbol Ω. If we plot a voltage-current graph we get a straight line indicating a linear relationship between voltage and current.
All conductors do not follow Ohm's law and exhibit a linear relationship between voltage and current. Let us learn about ohmic and non-ohmic conductors with examples and their characteristics.
Ohmic Conductors :
Electrical conductors which obey Ohm’s law are called Ohmic Conductors. The resistance of ohmic conductors is independent of applied voltage i.e., the resistance remains constant regardless of the magnitude of the applied voltage. They have a linear relationship between the current and the voltage.
Ohmic conductors obey Ohm's law until the physical conditions like pressure and the temperature of the conductor are in the rated range. Because when the temperature of a conductor increases, atoms start vibrating heavily due to which the electrons attempting to pass through the conductor collide with other electrons. This collision uses up some energy from the free electrons, causing more resistance when there is an increase in the temperature.
Thus conductors obey Ohm's law when the pressure and the temperature remain constant otherwise they become non-ohmic conductors. The resistance of the conductor is given by the ratio of voltage to current.
V-I Characteristic of Ohmic Conductors :
The V-I characteristic of a conductor is obtained by plotting a graph for values of current flowing through a conductor for the corresponding values of potential difference as shown in the below figure. It can be seen that the V-I graph for an ohmic conductor is a linear or straight line passing through the origin.
The slope of this V-I graph gives the value of resistance and it remains constant for ohmic conductors. The V-I graph of ohmic conductors with low resistance has a shallow slope, whereas the V-I graph of ohmic conductors with high resistance has a steep slope.
Examples of Ohmic Conductors :
Some examples of ohmic conductors are metals and resistors.
Resistor :
A resistor is a good example of an ohmic conductor. It is a basic electrical component used to control the flow of electricity in a circuit. The voltage drop across a resistor is directly proportional to the current that is flowing, being a constant resistance.
Resistors have a linear relationship between voltage and current. However, there are some types of resistors that do not obey Ohm's law and are considered non-ohmic conductors.
Metals :
Most of the metals like copper, silver, gold, aluminum, etc, are good conductors and obey Ohm's law at normal voltages and currents. They exhibit a linear relationship between the voltage across them and the current flowing through them. Under normal operating conditions, the heat developed is low maintaining a constant temperature and thus resistance remains constant.
Non-Ohmic Conductors :
Electrical conductors that do not obey Ohm’s law are called Non-Ohmic Conductors. In other words, non-ohmic conductors have a non-linear relationship between voltage and current i.e., voltage is no more proportional to current. The resistance of non-ohmic conductors depends upon the applied voltage i.e., the value of resistance varies with the voltage applied.
Since non-ohmic conductors do not follow Ohm's law they are characterized by their resistance which depends upon applied voltage. Even though non-ohmic conductors exhibit a non-linear relationship they have their own specialized uses in various electrical and electronic applications.
Examples of Non-Ohmic Conductors :
Some examples of non-ohmic conductors are filament lamps, thermistors, semiconductors like diodes, thyristors, transistors, etc.
PN Junction Diode :
A diode is a semiconductor device that allows current to flow easily in one direction and blocks the flow of current in the opposite direction. It is made up of two differently doped layers of semiconductor material that form a PN junction. Below shows the V-I characteristics of a diode.
In the above graph, it can be seen that the slope is not a straight line which leads us to understand there is no direct proportional relationship between current and voltage. In the forward-biased condition of the diode, the current flowing through the diode increases exponentially with the increase in the forward voltage.
In the reverse-biased condition of the diode, the current flowing through the diode is very small and almost constant, regardless of the increase in the reverse voltage. Therefore, a diode is a non-ohmic conductor because its V-I characteristics are not linear. Other semiconductors like transistors, thyristors, etc, are also examples of non-ohmic conductors which have non-linear relationships.
Incandescent Bulb :
An incandescent bulb is a type of filament lamp which produces light by heating a filament made up of metals that possess nonlinear characteristics. The heat generated by the filament makes the bulb to have non-linear characteristics. Since the filament in the light bulb is made up of conducting material, it has naturally low resistance.
When a voltage is applied across the incandescent lamp, high current flows through the filament due to negligible resistance. The flow of high current increases the temperature of the filament, which causes a change in resistance. However the current reduces due to an increase in resistance and the lamp operates normally.
If we plot the V-I graph for the above operation of incandescent bulb it produces a characteristic non-linear current-voltage relationship. The current increases at a proportionally slower rate than the potential difference. Thus a filament bulb is considered a non-ohmic conductor.
Difference between Ohmic and Non-Ohmic Conductors :
| Ohmic Conductors | Non-ohmic Conductors | |
|---|---|---|
| Definition | The type of conductors that obey Ohm's law are called Ohmic Conductors. | The type of conductors which do not obey Ohm's law are called as Non-Ohmic Conductors. |
| Effect on Resistance | Ohmic conductors have a constant electrical resistance over a wide range of voltages and currents. | The resistance of the non-ohmic conductor changes with changes in voltage and current. |
| Linearity | The relationship between current and voltage is linear. | The relationship between current and voltage is not linear. |
| V-I Slope | The voltage-current graph of ohmic conductors will be a straight line. | The voltage-current graph of non-ohmic conductors will be a curved line. |
| Examples | Examples of ohmic conductors are metals, resistors, etc. | Examples of non-ohmic conductors are diodes, transistors, thyristors, semiconductors, filament bulbs, etc. |
Conclusion :
Therefore, ohmic and non-ohmic are two different types of behavior in conductors. A conductor whose resistance remains constant and does not depend upon the applied voltage is called an ohmic conductor, whereas a conductor whose resistance varies with a change in the applied voltage is called a non-ohmic conductor.
Ohmic conductors are used as connecting wires in electrical and electronics circuits as they offer better control of the current flow. Whereas the non-linear characteristics of non-ohmic conductors make them used in different applications like filament blub, temperature sensing, voltage regulation, etc.
