Understanding Ohms Law: Application To Diodes Explained

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. However, this law does not apply to all materials. For example, a diode is a non-ohmic device and does not follow Ohm's law. This is because a diode is a circuit device that allows current flow in only one direction.

Ohm's Law and its limitations

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, we arrive at the usual mathematical equation that describes this relationship:

> I = V/R, where I is the current through the conductor in units of amperes, V is the voltage measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.

However, Ohm's law does not apply to all materials. It is not a law of nature like Newton's laws or the laws of thermodynamics. It is an empirical law, an experimentally observed phenomenon.

Any material, component, or device that obeys Ohm's law, where the current through the device is proportional to the voltage applied, is known as an ohmic material or ohmic component. Any material or component that does not obey Ohm's law is known as a nonohmic material or nonohmic component.

A diode is a nonohmic device. It is a semiconducting circuit element that allows current flow in only one direction. A plot of current versus voltage for a diode shows a non-linear relationship.

Ohm's law is commonly stated as V = IR, but it was originally stated in terms of the current density, the conductivity, and the electrical field. This microscopic view suggests the proportionality V ∝ I comes from the drift velocity of the free electrons in the metal that results from an applied electrical field.

Ohm's law is widely used in physics, particularly in electrical and electronics fields. It is important for several reasons:

• By varying the number of resistors, you can regulate the quantity of current travelling through the circuit. Higher resistors mean a lower supply of current.
• It helps estimate the power of a circuit using the equation P = VI, where P represents electric energy. This value indicates the amount of energy transferred each second.
• Ohm's law can be used with Kirchhoff's voltage theory to estimate the total voltage fall throughout the elements of a system.

Ohm's law has several everyday applications, including:

• Fan controllers, which allow us to adjust the fan's power.
• Immersion heaters, which feature a high-resistance metallic coil that permits a specific amount of energy to flow through it and generates warmth.
• Electric kettles and irons, which use Ohm's law to assist in creating the needed quantity of temperature by modifying the excessive inflow of electricity with resistors.

Limitations of Ohm's Law

Ohm's law does not apply to circuits when current flows in only one direction. These circuits are known as unilateral systems. Diodes, transistors, and other similar circuits are examples of such devices.

For Ohm's law to be valid, the current carried inside the conductor must be directly proportional to the voltage between the two sites at every moment. This also indicates that the circuit's resistivity must be constant.

Ohm's law is not applicable to all materials. It does not apply to non-linear components. Non-ohmic wires are conductors that do not follow Ohm's law. Semiconductors such as germanium and silicon break Ohm's law.

Ohm's law is also not valid when temperature varies. It is only applicable when temperature and other physical conditions have no effect on the resistivity of metallic conductors. For example, it does not apply to the filament in an incandescent lightbulb, as the resistance of the filament changes as it heats up.

Ohm's law does not apply to nonmetallic wires. In the event of intricate circuits, calculating Ohm's law might be tricky.

Ohm's Law's restrictions

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, we arrive at the usual mathematical equation that describes this relationship:

> I = V/R, where I is the current through the conductor in units of amperes, V is the voltage measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms.

Ohm's Law is not considered a law of nature, and it does not apply to all materials. Any material or component that does not obey Ohm's Law is known as a nonohmic material or component.

A diode is a nonohmic device. It is a circuit device that allows current flow in only one direction. A diode consists of an anode and a cathode. When the anode is at a negative potential and the cathode is at a positive potential, the diode is said to have reverse bias, and there is very little current flow through the diode and the resistor. When the battery and the potential across the diode are reversed, making the anode positive and the cathode negative, the diode conducts and current flows through the diode if the voltage is greater than 0.7 V.

The resistance of the diode is close to zero, but as the voltage applied increases, the current through the diode increases, but the voltage across the diode remains approximately 0.7 V. Thus, the voltage and the current do not have a linear relationship, and the diode is an example of a nonohmic device.

Ohm's Law does not apply to circuits when current flows in only one direction, such as those containing diodes, transistors, and other similar circuits. For Ohm's Law to be valid, the current carried inside the conductor must be directly proportional to the voltage between the two sites at every moment, and the circuit's resistivity must be constant.

Ohm's Law is widely used in physics, particularly in electrical and electronics fields. It is important for several reasons, including helping to regulate the amount of current travelling through a circuit and assisting in estimating the power of a circuit.

Examples of the limitations of Ohm's Law

Ohm's law states that the current flowing in a conductor is directly proportional to the potential difference across its ends, provided the physical conditions and temperature of the conductor remain constant.

However, Ohm's law has its limitations and does not apply to all electrical components. Here are some examples of the limitations of Ohm's law:

• Unilateral Networks: Ohm's law is not applicable to unilateral networks, which allow current to flow in only one direction. Such networks consist of elements like diodes, transistors, etc. These components only permit current to flow in one direction, and hence, Ohm's law cannot be used to determine the relationship between voltage and current.
• Non-linear Elements: The law does not apply to non-linear elements, which do not exhibit a constant resistance value. In other words, their resistance changes with different values of voltage and current. An example of a non-linear element is a thyristor.
• Semiconductors: Semiconductors, such as Silicon and Germanium, are known as non-ohmic conductors and do not obey Ohm's law.
• Non-constant Voltage: Ohm's law assumes a constant voltage with respect to time. However, for non-linear electrical components with properties like capacitance and resistance, the voltage level will not remain constant, making it problematic to apply Ohm's law.

Why Ohm's Law doesn't apply to diodes

Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. In other words, the current is equal to the voltage divided by the resistance: I = V/R.

A diode is a non-ohmic device, meaning it does not follow Ohm's law. This is because the resistance of a diode changes depending on the applied current or voltage. As a result, you cannot simply use the equation V=IR to determine the relationship between voltage and current, as you would with a resistor.

Ohm's law is a linear equation, and diodes exhibit a non-linear relationship between voltage and current. This can be seen in a plot of current versus voltage for a diode, where the voltage and current do not have a linear relationship.

Diodes are unilateral electrical components, meaning they only allow current to flow in one direction. For Ohm's law to be valid, the current carried in the conductor must be directly proportional to the voltage between the two points at all times, and the resistance must be constant.

Ohm's law is still a useful concept, however, as it applies to many other materials and can be used to calculate the power of a circuit using the equation P=VI, where P represents electric power.

The importance of Ohm's Law

Ohm's Law is a fundamental principle in electrical engineering and physics that describes the relationship between current, voltage, and resistance in a system. It is a simple yet powerful tool for designing and analyzing electrical systems and is considered one of the most important equations when it comes to understanding electric circuits. Here are a few reasons why Ohm's Law is so important:

Calculating Unknown Values

Ohm's Law allows technicians and engineers to calculate unknown values in an electrical circuit. If two values are known, Ohm's Law can be used to calculate the third. For example, if you know the voltage and current in a circuit, you can use Ohm's Law to determine the resistance. This is especially useful when resistance cannot be measured directly in an operating circuit.

Controlling Current

Ohm's Law enables you to control the amount of current in a circuit. By adding or removing resistors, you can increase or decrease the current flow, respectively. This is crucial for ensuring that components in a circuit receive the optimal amount of current.

Analyzing Circuit Diagrams

Ohm's Law is essential for analyzing circuit diagrams, especially when combined with Kirchhoff's laws. It allows you to calculate the voltage drop across any component in a circuit, making it a valuable tool for electronics classes and troubleshooting electrical systems.

Ensuring Safety

Ohm's Law has important implications for the safety of electrical systems. By calculating the expected current flow and voltage drop, engineers can design systems that are safe and reliable. If the voltage is too high, it can cause the current to exceed the capacity of conductors and components, leading to overheating, damage, and even fires.

Power Distribution System Design

Ohm's Law is critical in the design and analysis of power distribution systems. It helps engineers calculate the expected current flow and voltage drop in components like power transmission lines and transformers, ensuring they are appropriately sized and rated to handle the load of the system.

Electronic Device Development

Ohm's Law plays a significant role in the development of electronic devices such as transistors, diodes, and integrated circuits. It helps engineers determine the appropriate size and rating of electrical components, ensuring they can handle the current and voltage in the circuit.

Limitations

It is important to note that Ohm's Law has some limitations. It assumes that the conductor has a linear resistance, which means the resistance remains constant regardless of the current. In reality, many conductors have nonlinear resistance characteristics, which can lead to unexpected behaviour in the circuit. Additionally, Ohm's Law is most applicable to DC circuits or circuits with constant voltage and current. In AC circuits, the behaviour can be more complex and difficult to predict.

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