Have you ever heard of the terms “ohmic” and “non-ohmic” before? If you’re not an electrical engineer or a physics enthusiast, the answer is probably no. But don’t worry, because understanding the difference between these two concepts is actually simpler than you might think. In short, ohmic materials are substances whose resistance remains constant irrespective of the voltage and current flowing through them. On the other hand, non-ohmic materials are substances whose resistance changes with the voltage or current that is applied to them.
What does this mean in practical terms? Well, let’s take an example. Imagine you have a light bulb that is made of an ohmic material. When you turn on the switch, the amount of current flowing through the bulb will be directly proportional to the voltage applied to it. This is because the bulb has a fixed resistance that doesn’t change with the amount of electricity passing through it. However, if the bulb was made of a non-ohmic material, things would be different. In this case, the amount of current flowing through the bulb would depend on the amount of voltage applied to it, because the resistance of the material changes with the electrical conditions.
So why does this matter? Well, ohmic and non-ohmic behavior can have a big impact on the performance of electrical circuits and devices. For instance, ohmic materials are often used as resistors in circuits where a steady amount of resistance is needed. Non-ohmic materials, on the other hand, can be used in devices that require a varying amount of resistance, such as surge protectors or temperature sensors. By understanding the difference between these two types of behavior, you can gain a deeper appreciation of how electrical systems work and how they can be optimized for different applications.
Conductivity of Materials
Conductivity refers to the ability of a material to conduct electricity. Materials can be classified into two types based on their conductivity: conductors and insulators. Conductors are materials that allow electric charges to flow freely through them, while insulators are materials that do not allow electric charges to flow easily. The conductivity of a material depends on several factors, including the type of material, its state (solid, liquid, or gas), and the temperature and pressure it is subjected to.
- Conductors: Some examples of conductors include metals such as copper, aluminum, and gold. These materials have a high concentration of free electrons, which allow electric charges to move freely through them. In general, the conductivity of metals decreases as temperature increases due to an increase in the number of collisions between free electrons and the vibrating atoms in the material.
- Insulators: Some examples of insulators include wood, rubber, and plastic. These materials do not have a high concentration of free electrons and therefore do not allow electric charges to flow easily through them. The conductivity of insulators also depends on factors such as their molecular structure and the presence of impurities.
The conductivity of a material can be measured in siemens per meter (S/m) or ohms per meter (Ω/m). Conductivity can also be expressed as resistance, which is the opposition of a material to the flow of electric current. It is often measured in ohms (Ω), and materials can be classified into two categories based on their behavior when an electric field is applied to them: ohmic and nonohmic materials.
| Ohmic Materials | Nonohmic Materials |
|---|---|
| Materials that follow Ohm’s law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points. | Materials that do not follow Ohm’s law and have a varying resistance as the voltage across them changes. |
| Examples of ohmic materials include metals and some conductive solutions. | Examples of nonohmic materials include semiconductors, diodes, and transistors. |
Understanding the conductivity of materials is important in the design and implementation of electrical circuits and devices. Conductive materials are used in wiring and electronic components, while insulators are used to protect against electrical shock and to prevent short circuits.
Resistance and Resistivity
Resistance is the measure of how much a material opposes the flow of electric current. It is determined by the nature of the material, its temperature, and its physical dimensions. The unit of resistance is ohm, and it is denoted by the symbol Ω (omega).
Resistivity, on the other hand, is the inherent tendency of a material to resist electric current flowing through it. It is a fundamental property of a material and is a measure of how well or poorly that material conducts electricity. Resistivity is denoted by the symbol ρ (rho), and its unit is ohm-meter (Ω.m).
- Resistance is dependent on the length, cross-sectional area, and the type of material, while resistivity is determined solely by the material.
- Resistance is a scalar quantity, while resistivity is a tensor quantity (it has direction as well as magnitude).
- Resistance is used to quantify the opposition of a device or a component to electric current, while resistivity is used to quantify the intrinsic nature of the material.
Materials that exhibit ohmic behavior have a constant resistance regardless of the applied voltage. Graphically, this behavior is represented as a straight line. However, materials exhibiting non-ohmic behavior have a non-linear resistance, and their resistance changes with the applied voltage. Graphically, this is represented as a curved line.
| Ohmic Materials | Non-Ohmic Materials |
|---|---|
| Metallic Conductors | Diodes and Transistors |
| Carbon Resistors | Thermistors |
| Electrolytes | Gas Discharge Tubes |
In summary, resistivity is an intrinsic property of a material while resistance is a measure of a device or a component’s opposition to electric current. Ohmic materials have a constant resistance, while non-ohmic materials have a non-linear resistance and their resistance changes with the applied voltage.
Electric current and voltage
Electricity is the flow of electric charge, and the movement of electrons is the basis of electric current. Electric current is the rate at which electric charge flows past a point in a circuit. It is measured in amperes (A), and it is denoted by the symbol “I.” Electric current is essential for the operation of electrical appliances, and it is the basis for the functioning of electrical power generation, distribution, and utilization systems. There are two types of electric current, direct current (DC), and alternating current (AC).
Voltage is the electric potential difference between two points in an electrical circuit, and it is the force that drives the flow of electric current in the circuit. It is measured in volts (V), and it is denoted by the symbol “V.” The voltage across a circuit element determines the amount of current that flows through it. Voltage is the primary means by which electrical energy is transmitted from one point to another in an electrical system.
Ohmic vs. Non-ohmic
- Ohmic Conductors: Ohmic conductors are electrical conductors that exhibit a linear relationship between electric current and voltage. The resistance of an ohmic conductor is constant and does not vary with the current or voltage. Examples of ohmic conductors include metals such as copper, aluminium, and silver.
- Non-ohmic Conductors: Non-ohmic conductors are electrical conductors that do not exhibit a linear relationship between electric current and voltage. The resistance of a non-ohmic conductor varies with the current or voltage. Examples of non-ohmic conductors include semiconductors, insulators, and some types of gases.
Resistance and Ohm’s Law
Resistance is the opposition to the flow of electric current in an electrical circuit, and it is measured in ohms (Ω). Resistance is the property of the conductor that determines how much current will flow through it for a given voltage. Ohm’s law states that the current flowing through a conductor is directly proportional to the voltage applied across it, and inversely proportional to its resistance. The formula for Ohm’s law is I = V/R, where I is the current, V is the voltage, and R is the resistance of the conductor.
The relationship between current, voltage, and resistance can be represented by a circuit diagram, which is a graphical representation of an electrical circuit. The circuit diagram shows the arrangement of circuit components and the flow of current in the circuit. The circuit diagram also shows the voltage across each component in the circuit.
| Symbol | Description | Unit |
|---|---|---|
| I | Electric Current | Amperes (A) |
| V | Electric Voltage | Volts (V) |
| R | Electric Resistance | Ohms (Ω) |
Understanding the difference between ohmic and non-ohmic conductors is crucial in the design and analysis of electrical and electronic systems. By knowing whether a material is an ohmic or non-ohmic conductor, engineers and technicians can determine the optimal operating conditions for the circuit components, and they can select the appropriate materials for the desired functionality of the circuit. Therefore, a working knowledge of electrical principles is essential for any electrical or electronic professional.
Ohm’s Law
Ohm’s law is perhaps one of the most fundamental laws in electronics. It states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points. In other words, the ratio of the voltage and the current is constant, represented by the letter “R” and is known as the resistance.
- Ohmic Conductors: In ohmic conductors, the ratio of the voltage and current remains constant, regardless of the amount of voltage applied, as long as the temperature and other physical conditions remain the same. Examples of ohmic conductors include metals like copper, gold, and silver.
- Non-Ohmic Conductors: In non-ohmic conductors, the ratio of the voltage and current is not constant but varies depending on the voltage applied and the physical conditions. Examples include semiconductors like silicon and germanium, where the relationship between voltage and current is not linear.
Non-ohmic conductors generally have a more complex relationship between voltage and current than ohmic conductors. In some cases, the current may increase more slowly than the voltage applied, or it may increase faster than the voltage applied. This relationship can be expressed using an I-V (current-voltage) curve.
Here is an example of an I-V curve for a non-ohmic conductor:
| Voltage (V) | Current (I) |
|---|---|
| 0 | 0 |
| 0.5 | 0.1 |
| 1 | 0.2 |
| 1.5 | 0.3 |
| 2 | 0.5 |
| 3 | 1 |
| 4 | 2.5 |
| 5 | 5 |
In this example, it is clear that the current does not increase linearly with the voltage applied. Instead, at low voltages, the current increases slowly, and then it begins to increase more rapidly. Eventually, it may reach a point where even small increases in voltage result in large changes in current.
Understanding the difference between ohmic and non-ohmic conductors is important for designing and troubleshooting electronic circuits, as different components and materials can behave in different ways.
Joule Heating Effect
When a current flows through a material, some of its energy is always converted into heat due to the resistance that the material offers to the flow of the current. This effect is known as the joule heating effect, named after James Prescott Joule who discovered it in the mid-19th century. The joule heating effect is the reason why toaster wires get hot when electric current is passed through them or why an electric iron becomes hot when it is used. In electrical circuits, the joule heating effect can also cause the temperature of the wires and other components to increase, which can eventually lead to their failure.
Ohmic versus Non-Ohmic materials
- An ohmic material is one that obeys Ohm’s law, which states that the current flowing through a material is directly proportional to the voltage applied across it, provided the temperature and other physical conditions remain constant. The resistance of an ohmic material is independent of the applied voltage or current.
- Non-ohmic materials, on the other hand, do not obey Ohm’s law and their resistance changes with the applied voltage or current. This usually happens when the current through the material is high and the temperature of the material increases due to the joule heating effect.
Effects of Joule Heating
The joule heating effect can cause several effects on the material through which the current flows. The most common effects of joule heating include:
- Temperature rise: As mentioned earlier, the joule heating effect leads to a temperature rise in the material, which can cause it to expand, deform, or even melt if the temperature gets too high. Therefore, joule heating needs to be considered when designing electrical systems to ensure that the material does not get too hot and cause any damage.
- Changes in resistance: The resistance of a material can change due to joule heating, especially in non-ohmic materials. This can lead to variations in the current flowing through the material and ultimately affect the performance of the electrical system.
- Electromigration: When the temperature of a conductor increases due to the joule heating effect, the atoms in the conductor may start to move from one place to another, leading to material degradation or even failure over time. This effect is known as electromigration.
The Relationship between Joule Heating and Power Dissipation
The Joule heating effect is related to the power dissipation of a material, which is the rate at which energy is converted into heat per unit time. The power dissipation in a material can be calculated using the formula:
| P | = | I²R |
Where P is the power dissipation, I is the current flowing through the material, and R is the resistance of the material. From this equation, we can see that the power dissipation increases as the current flowing through the material or the resistance of the material increases. This is why thick wires are used in high current applications to avoid overheating due to the Joule heating effect.
Semiconductors and insulators
When it comes to the difference between ohmic and non-ohmic materials, it’s important to consider the characteristics of semiconductors and insulators. Semiconductors are materials that have electrical conductivity between conductors (like metal) and insulators (like rubber). This means that their conductivity can be easily modified by changing their temperature, doping, or exposure to light. Insulators, on the other hand, are materials that resist the flow of electric current due to their tightly bound electrons, making them non-conductive.
- Semiconductors: Semiconductors are materials that can have both ohmic and non-ohmic behavior, depending on their doping levels and temperature. Doping refers to the addition of impurities to the semiconductor, which can either increase or decrease its conductivity. When a semiconductor is doped with impurities that add electrons (n-type), its conductivity increases, making it ohmic. When it is doped with impurities that remove electrons (p-type), its conductivity decreases, making it non-ohmic. Temperature also plays a role in the conductivity of semiconductors. As the temperature of a semiconductor increases, so does its conductivity, making it closer to ohmic behavior.
- Insulators: Insulators are non-ohmic materials because they do not conduct electricity easily. This is because their tightly bound electrons do not allow for the free movement of electrons needed for conductivity. However, at very high voltages, insulators can experience a phenomenon called breakdown, where their resistance suddenly drops and they become conductive. This is why insulators are used for electrical safety, as they can prevent current from flowing through them and potentially causing harm.
Understanding the behavior of semiconductors and insulators is crucial in the field of electronics, as many devices such as transistors and diodes rely on their properties for operation. By properly manipulating the conductivity of these materials, engineers and scientists can create electronic circuits that are efficient, reliable, and safe.
For a closer look at the properties of semiconductors and insulators, see the table below:
| Property | Semiconductors | Insulators |
|---|---|---|
| Conductivity | Easily modified by doping and temperature | Resistant to the flow of electric current |
| Breakdown voltage | Low | Very high |
| Applications | Transistors, diodes, solar cells, LEDs | Electrical insulation, safety barriers |
Real-life applications of ohmic and non-ohmic behavior
Understanding the difference between Ohmic and non-Ohmic behavior is essential for understanding many everyday devices. Here are some real-life examples:
- Ohmic behavior
- Light bulbs: Incandescent bulbs use Ohmic metals like tungsten, which heats up, and the resistance increases as the current flows.
- Heating elements: The heating elements in stoves and ovens use Ohmic behavior to convert electric energy into heat energy.
- Electric circuits: Ohmic behavior dictates how electric circuits work, and Ohm’s law helps us predict the flow of current in a circuit.
- Non-Ohmic behavior
- Diodes: The characteristic curve of a diode is non-linear, which means the resistance changes nonlinearly concerning the current.
- Thermistors: Thermistors use non-Ohmic behavior, and their resistance dramatically changes concerning the surrounding temperature.
- Gas discharge lamps: Gas discharge lamps, such as fluorescent lights, neon lamps, etc., have non-Ohmic behavior because their resistance depends upon the gas inside the lamp.
Non-Ohmic behavior is essential in devices like diodes, as they allow for the control of electrical currents and voltages. Thermal resistors changing resistance according to the temperature is useful for applications such as temperature sensors, while gas discharge lamps are used in advertising and decoration.
To better understand Ohmic and non-Ohmic behavior, it can help to visualize them in a chart. The chart shows an inverse relationship between resistance and temperature. An Ohmic metal (such as tungsten) displays a linear upward trend in resistance. On the other hand, a non-Ohmic element like a thermistor displays a nonlinear path, indicating that the resistance changes differently concerning temperature compared to an Ohmic metal.
| Characteristics | Ohmic | Non-Ohmic |
|---|---|---|
| Resistance-temperature relationship | Linear | Nonlinear |
| Material used | Metals | Semiconductors, Insulators |
| Ohm’s Law | Applicable | Not applicable |
| Current-voltage relationship | Linear | Nonlinear |
Overall, understanding Ohmic and non-Ohmic behavior is a fundamental concept in physics and engineering. It helps better understand electricity and how devices and appliances function. Knowing the difference between Ohmic and non-Ohmic behavior will allow one to make informed decisions about devices and their applications in everyday situations.
What is the difference between ohmic and non-ohmic?
1. What does ohmic mean?
Ohmic means that the material follows Ohm’s law, where the current is directly proportional to the voltage. This means that as the voltage increases, the current increases at the same rate.
2. What does non-ohmic mean?
Non-ohmic means the material does not obey Ohm’s law when the voltage changes. This means that the current does not increase at the same rate as the voltage.
3. What causes a material to be non-ohmic?
A material is non-ohmic if it has a varying resistance with changes in temperature, magnetic fields, or light intensity. These factors result in the current not being directly proportional to the voltage.
4. What are some examples of ohmic materials?
Some examples of ohmic materials include metals like copper and aluminum. These materials have a consistent resistance, and the current increases linearly with the voltage.
5. What are some examples of non-ohmic materials?
Some examples of non-ohmic materials include semiconductors, diodes, and thermistors. These materials do not have a constant resistance and the current does not increase linearly with the voltage.
Closing thoughts
Now that you know the difference between ohmic and non-ohmic materials, you can understand why materials behave differently in electrical circuits. Understanding these concepts is essential for designing and building electronic devices. Thanks for reading, and be sure to visit again for more insights on electronics and technology!