What devices do not follow Ohms law?
2 Answers
Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points, assuming the temperature and material properties remain constant. The relationship is typically represented as \( V = IR \), where \( V \) is the voltage, \( I \) is the current, and \( R \) is the resistance.
However, not all devices or components strictly follow Ohm's Law. Devices that do not obey Ohm's Law are generally characterized by their non-linear relationships between voltage and current. Here are some common examples:
### 1. **Semiconductors**
- **Diodes**: Diodes allow current to flow in one direction only. The relationship between the voltage across a diode and the current through it is exponential, not linear. This is described by the diode equation: \( I = I_s (e^{V/(nV_T)} - 1) \), where \( I_s \) is the saturation current, \( V \) is the voltage, \( V_T \) is the thermal voltage, and \( n \) is the ideality factor.
- **Transistors**: Transistors (both bipolar junction transistors and field-effect transistors) have complex voltage-current relationships that are dependent on their operating mode and biasing conditions. For example, in a bipolar junction transistor, the base-emitter junction behaves like a diode, and the collector current is influenced by the base current in a non-linear manner.
### 2. **Non-Ohmic Materials**
- **Superconductors**: In the superconducting state, materials exhibit zero electrical resistance, meaning that they can carry an electric current indefinitely without any voltage drop. The relationship between voltage and current is not linear in this state, as Ohm’s Law does not apply.
- **Non-Ohmic Conductors**: Some materials and substances have a resistance that varies with the applied voltage or current, making their behavior non-linear. For example, certain types of carbon-based materials, like some forms of graphite or carbon nanotubes, may show non-linear I-V characteristics.
### 3. **Components with Non-Linear Characteristics**
- **Varistors**: Also known as voltage-dependent resistors, varistors have a resistance that varies significantly with the applied voltage. Their I-V characteristics are non-linear and can be described by an exponential relationship.
- **Thermistors**: Thermistors are resistors whose resistance changes significantly with temperature. They come in two main types: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). Their resistance-temperature relationship is non-linear.
### 4. **Light Emitting Diodes (LEDs)**
- LEDs are a specific type of diode that emits light when current flows through them. The current-voltage relationship of an LED is exponential, similar to other diodes, and involves thresholds and knee points in their I-V characteristics.
### 5. **Non-Linear Resistors**
- Some resistors, like those used in specific electronic circuits for nonlinear behavior, do not follow Ohm’s Law because their resistance changes with voltage or current in a non-linear fashion.
In summary, devices and materials that exhibit non-linear relationships between voltage and current do not follow Ohm's Law. This non-linearity can be due to the intrinsic properties of the materials or the specific design and function of the devices.
However, not all devices or components strictly follow Ohm's Law. Devices that do not obey Ohm's Law are generally characterized by their non-linear relationships between voltage and current. Here are some common examples:
### 1. **Semiconductors**
- **Diodes**: Diodes allow current to flow in one direction only. The relationship between the voltage across a diode and the current through it is exponential, not linear. This is described by the diode equation: \( I = I_s (e^{V/(nV_T)} - 1) \), where \( I_s \) is the saturation current, \( V \) is the voltage, \( V_T \) is the thermal voltage, and \( n \) is the ideality factor.
- **Transistors**: Transistors (both bipolar junction transistors and field-effect transistors) have complex voltage-current relationships that are dependent on their operating mode and biasing conditions. For example, in a bipolar junction transistor, the base-emitter junction behaves like a diode, and the collector current is influenced by the base current in a non-linear manner.
### 2. **Non-Ohmic Materials**
- **Superconductors**: In the superconducting state, materials exhibit zero electrical resistance, meaning that they can carry an electric current indefinitely without any voltage drop. The relationship between voltage and current is not linear in this state, as Ohm’s Law does not apply.
- **Non-Ohmic Conductors**: Some materials and substances have a resistance that varies with the applied voltage or current, making their behavior non-linear. For example, certain types of carbon-based materials, like some forms of graphite or carbon nanotubes, may show non-linear I-V characteristics.
### 3. **Components with Non-Linear Characteristics**
- **Varistors**: Also known as voltage-dependent resistors, varistors have a resistance that varies significantly with the applied voltage. Their I-V characteristics are non-linear and can be described by an exponential relationship.
- **Thermistors**: Thermistors are resistors whose resistance changes significantly with temperature. They come in two main types: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC). Their resistance-temperature relationship is non-linear.
### 4. **Light Emitting Diodes (LEDs)**
- LEDs are a specific type of diode that emits light when current flows through them. The current-voltage relationship of an LED is exponential, similar to other diodes, and involves thresholds and knee points in their I-V characteristics.
### 5. **Non-Linear Resistors**
- Some resistors, like those used in specific electronic circuits for nonlinear behavior, do not follow Ohm’s Law because their resistance changes with voltage or current in a non-linear fashion.
In summary, devices and materials that exhibit non-linear relationships between voltage and current do not follow Ohm's Law. This non-linearity can be due to the intrinsic properties of the materials or the specific design and function of the devices.
Ohm's Law, which states that \( V = IR \) (voltage equals current times resistance), is a fundamental principle in electrical engineering. However, not all electronic devices or components follow this simple linear relationship. Here’s a detailed overview of devices and components that do not strictly adhere to Ohm’s Law:
### 1. **Semiconductors**
- **Diodes**: Diodes are devices that allow current to flow in only one direction. Their relationship between voltage and current is not linear. For example, a silicon diode has a threshold voltage (typically around 0.7V) below which it conducts very little current, and above which current increases exponentially with voltage.
- **Transistors**: Transistors, including both bipolar junction transistors (BJTs) and field-effect transistors (FETs), have complex relationships between voltage and current. The characteristic curves for these devices are nonlinear, reflecting their behavior as amplifiers or switches rather than simple resistors.
### 2. **Non-Ohmic Materials**
- **Thermistors**: Thermistors are temperature-sensitive resistors. Their resistance changes with temperature in a nonlinear manner. For example, Negative Temperature Coefficient (NTC) thermistors have resistance that decreases with increasing temperature, while Positive Temperature Coefficient (PTC) thermistors have resistance that increases with temperature.
- **Varistors**: Varistors, or voltage-dependent resistors, have resistance that varies with the applied voltage. They are used to protect circuits from voltage surges and have a nonlinear I-V (current-voltage) characteristic.
### 3. **Superconductors**
- **Superconducting Materials**: In their superconducting state, materials exhibit zero electrical resistance. This means that the relationship between voltage and current is fundamentally different from what Ohm’s Law describes for conventional resistors. Ohm’s Law is not applicable in the traditional sense for superconductors since the resistance is zero.
### 4. **Nonlinear Resistors**
- **Light-Dependent Resistors (LDRs)**: These resistors change their resistance based on the intensity of light falling on them. The relationship between light intensity and resistance is not linear, hence their behavior does not conform to Ohm's Law.
### 5. **Capacitors and Inductors**
- **Capacitors**: Capacitors store energy in an electric field and their behavior is described by the relationship \( I = C \frac{dV}{dt} \), where \( I \) is the current, \( C \) is the capacitance, and \( \frac{dV}{dt} \) is the rate of change of voltage. This relationship is clearly nonlinear, especially when considering dynamic circuits.
- **Inductors**: Inductors store energy in a magnetic field and their behavior is described by \( V = L \frac{dI}{dt} \), where \( L \) is the inductance and \( \frac{dI}{dt} \) is the rate of change of current. This means that the voltage-current relationship is nonlinear in circuits where current changes rapidly.
### 6. **Complex Nonlinear Devices**
- **Integrated Circuits (ICs)**: Many ICs, such as operational amplifiers, analog multipliers, and other complex semiconductor devices, do not follow Ohm's Law in a straightforward manner. Their behavior depends on various factors including feedback loops, non-linear components, and internal design.
### Summary
In summary, devices and components that do not follow Ohm’s Law are those whose resistance varies with applied voltage, current, or other external conditions. These include various semiconductor devices (like diodes and transistors), non-linear resistors (such as thermistors and varistors), capacitors, inductors, and complex integrated circuits. Understanding the behavior of these devices often requires more advanced models and equations beyond Ohm's Law.
### 1. **Semiconductors**
- **Diodes**: Diodes are devices that allow current to flow in only one direction. Their relationship between voltage and current is not linear. For example, a silicon diode has a threshold voltage (typically around 0.7V) below which it conducts very little current, and above which current increases exponentially with voltage.
- **Transistors**: Transistors, including both bipolar junction transistors (BJTs) and field-effect transistors (FETs), have complex relationships between voltage and current. The characteristic curves for these devices are nonlinear, reflecting their behavior as amplifiers or switches rather than simple resistors.
### 2. **Non-Ohmic Materials**
- **Thermistors**: Thermistors are temperature-sensitive resistors. Their resistance changes with temperature in a nonlinear manner. For example, Negative Temperature Coefficient (NTC) thermistors have resistance that decreases with increasing temperature, while Positive Temperature Coefficient (PTC) thermistors have resistance that increases with temperature.
- **Varistors**: Varistors, or voltage-dependent resistors, have resistance that varies with the applied voltage. They are used to protect circuits from voltage surges and have a nonlinear I-V (current-voltage) characteristic.
### 3. **Superconductors**
- **Superconducting Materials**: In their superconducting state, materials exhibit zero electrical resistance. This means that the relationship between voltage and current is fundamentally different from what Ohm’s Law describes for conventional resistors. Ohm’s Law is not applicable in the traditional sense for superconductors since the resistance is zero.
### 4. **Nonlinear Resistors**
- **Light-Dependent Resistors (LDRs)**: These resistors change their resistance based on the intensity of light falling on them. The relationship between light intensity and resistance is not linear, hence their behavior does not conform to Ohm's Law.
### 5. **Capacitors and Inductors**
- **Capacitors**: Capacitors store energy in an electric field and their behavior is described by the relationship \( I = C \frac{dV}{dt} \), where \( I \) is the current, \( C \) is the capacitance, and \( \frac{dV}{dt} \) is the rate of change of voltage. This relationship is clearly nonlinear, especially when considering dynamic circuits.
- **Inductors**: Inductors store energy in a magnetic field and their behavior is described by \( V = L \frac{dI}{dt} \), where \( L \) is the inductance and \( \frac{dI}{dt} \) is the rate of change of current. This means that the voltage-current relationship is nonlinear in circuits where current changes rapidly.
### 6. **Complex Nonlinear Devices**
- **Integrated Circuits (ICs)**: Many ICs, such as operational amplifiers, analog multipliers, and other complex semiconductor devices, do not follow Ohm's Law in a straightforward manner. Their behavior depends on various factors including feedback loops, non-linear components, and internal design.
### Summary
In summary, devices and components that do not follow Ohm’s Law are those whose resistance varies with applied voltage, current, or other external conditions. These include various semiconductor devices (like diodes and transistors), non-linear resistors (such as thermistors and varistors), capacitors, inductors, and complex integrated circuits. Understanding the behavior of these devices often requires more advanced models and equations beyond Ohm's Law.