Why do non ohmic conductors not follow Ohms law?
2 Answers
Non-ohmic conductors do not follow **Ohm's Law** because their resistance changes with factors such as **temperature**, **voltage**, or **current**. Ohm's Law, which states \( V = IR \) (voltage equals current times resistance), assumes that the resistance \( R \) is constant. This assumption holds true for **ohmic conductors** like metals under steady conditions, where the relationship between voltage and current remains linear. However, in non-ohmic conductors, the relationship between voltage and current is **non-linear** due to the following reasons:
### 1. **Temperature Dependency**
In materials like semiconductors, diodes, or filament bulbs, the **resistance changes with temperature**. For example:
- **Filament bulbs**: As current increases, the filament heats up, and its resistance rises. This leads to a non-linear voltage-current relationship.
- **Semiconductors**: In diodes or transistors, the flow of current significantly depends on temperature, which causes a variation in resistance as the temperature changes.
### 2. **Electric Field Effects**
Some materials, like **semiconductors**, exhibit non-linear behavior because the **electric field affects their charge carriers**. For instance, in diodes, the current flows easily in one direction but not in the reverse direction, causing a deviation from Ohm's Law.
### 3. **Saturation of Charge Carriers**
In devices such as transistors, the number of charge carriers (like electrons) involved in current flow can become saturated. This means that after a certain point, increasing the voltage no longer results in a proportional increase in current, which deviates from Ohm's Law.
### 4. **Non-Linear Devices**
Devices like **diodes, LEDs, transistors**, and **zener diodes** are designed to operate in specific conditions where current-voltage characteristics are inherently non-linear. For example:
- **Diode**: In forward bias, a diode allows current to pass after a certain threshold voltage, and the current increases rapidly with a small increase in voltage. In reverse bias, the current is almost zero up to a certain breakdown voltage, showing a non-linear characteristic.
### Summary:
Non-ohmic conductors do not follow Ohm's Law due to varying resistance, which is influenced by external factors like temperature, electric fields, or saturation of charge carriers. These materials exhibit non-linear current-voltage characteristics that differ from the constant resistance assumed in Ohm's Law.
### 1. **Temperature Dependency**
In materials like semiconductors, diodes, or filament bulbs, the **resistance changes with temperature**. For example:
- **Filament bulbs**: As current increases, the filament heats up, and its resistance rises. This leads to a non-linear voltage-current relationship.
- **Semiconductors**: In diodes or transistors, the flow of current significantly depends on temperature, which causes a variation in resistance as the temperature changes.
### 2. **Electric Field Effects**
Some materials, like **semiconductors**, exhibit non-linear behavior because the **electric field affects their charge carriers**. For instance, in diodes, the current flows easily in one direction but not in the reverse direction, causing a deviation from Ohm's Law.
### 3. **Saturation of Charge Carriers**
In devices such as transistors, the number of charge carriers (like electrons) involved in current flow can become saturated. This means that after a certain point, increasing the voltage no longer results in a proportional increase in current, which deviates from Ohm's Law.
### 4. **Non-Linear Devices**
Devices like **diodes, LEDs, transistors**, and **zener diodes** are designed to operate in specific conditions where current-voltage characteristics are inherently non-linear. For example:
- **Diode**: In forward bias, a diode allows current to pass after a certain threshold voltage, and the current increases rapidly with a small increase in voltage. In reverse bias, the current is almost zero up to a certain breakdown voltage, showing a non-linear characteristic.
### Summary:
Non-ohmic conductors do not follow Ohm's Law due to varying resistance, which is influenced by external factors like temperature, electric fields, or saturation of charge carriers. These materials exhibit non-linear current-voltage characteristics that differ from the constant resistance assumed in Ohm's Law.
Non-ohmic conductors do not follow Ohm's Law because their resistance changes with the applied voltage or current. Here's a detailed explanation:
### Ohm's Law
Ohm's Law states that for a conductor, the current (\(I\)) passing through it is directly proportional to the voltage (\(V\)) across it, given a constant resistance (\(R\)):
\[ V = I \cdot R \]
### Non-Ohmic Conductors
In non-ohmic conductors, this relationship does not hold true. The reasons for this deviation can include:
1. **Variable Resistance with Voltage:**
- **Semiconductors:** In materials like silicon or germanium, the resistance varies significantly with the applied voltage. For example, in a diode, the current increases exponentially with the voltage once a certain threshold is crossed.
- **Zener Diodes:** These components exhibit a constant voltage drop in reverse bias once a certain breakdown voltage is reached, thus deviating from Ohm's Law.
2. **Temperature Effects:**
- In many materials, resistance increases with temperature. For instance, in a filament lamp (incandescent bulb), the filament's temperature rises significantly as current flows, leading to a nonlinear relationship between voltage and current.
3. **Material Properties:**
- **Superconductors:** At temperatures below their critical point, superconductors exhibit zero resistance, leading to an entirely different electrical behavior compared to ordinary conductors.
- **Nonlinear Resistors:** Components like thermistors and varistors have resistance that varies nonlinearly with temperature or voltage.
4. **Nonlinear I-V Characteristics:**
- Non-ohmic conductors often exhibit nonlinear current-voltage (I-V) characteristics. For example, in a transistor, the current through the device depends on the voltage across it and other factors like the gate voltage (in FETs).
5. **Physical Effects:**
- **Nonlinear Effects:** Some materials exhibit nonlinear effects such as piezoelectric effects, where mechanical stress changes the electrical resistance, or magnetic effects in magnetoresistors.
### Examples of Non-Ohmic Behavior
- **Diodes:** They allow current to flow easily in one direction but restrict it in the opposite direction, showing a nonlinear I-V characteristic.
- **Transistors:** The current flow through a transistor depends on multiple factors, including the base-emitter voltage in a BJT or the gate voltage in a MOSFET.
- **Filament Lamps:** As the filament heats up, its resistance increases, resulting in a non-linear relationship between voltage and current.
In summary, non-ohmic conductors deviate from Ohm's Law because their resistance changes with factors like voltage, current, temperature, and material properties. This results in a nonlinear relationship between voltage and current, unlike ohmic conductors where resistance remains constant over a range of applied voltages and currents.
### Ohm's Law
Ohm's Law states that for a conductor, the current (\(I\)) passing through it is directly proportional to the voltage (\(V\)) across it, given a constant resistance (\(R\)):
\[ V = I \cdot R \]
### Non-Ohmic Conductors
In non-ohmic conductors, this relationship does not hold true. The reasons for this deviation can include:
1. **Variable Resistance with Voltage:**
- **Semiconductors:** In materials like silicon or germanium, the resistance varies significantly with the applied voltage. For example, in a diode, the current increases exponentially with the voltage once a certain threshold is crossed.
- **Zener Diodes:** These components exhibit a constant voltage drop in reverse bias once a certain breakdown voltage is reached, thus deviating from Ohm's Law.
2. **Temperature Effects:**
- In many materials, resistance increases with temperature. For instance, in a filament lamp (incandescent bulb), the filament's temperature rises significantly as current flows, leading to a nonlinear relationship between voltage and current.
3. **Material Properties:**
- **Superconductors:** At temperatures below their critical point, superconductors exhibit zero resistance, leading to an entirely different electrical behavior compared to ordinary conductors.
- **Nonlinear Resistors:** Components like thermistors and varistors have resistance that varies nonlinearly with temperature or voltage.
4. **Nonlinear I-V Characteristics:**
- Non-ohmic conductors often exhibit nonlinear current-voltage (I-V) characteristics. For example, in a transistor, the current through the device depends on the voltage across it and other factors like the gate voltage (in FETs).
5. **Physical Effects:**
- **Nonlinear Effects:** Some materials exhibit nonlinear effects such as piezoelectric effects, where mechanical stress changes the electrical resistance, or magnetic effects in magnetoresistors.
### Examples of Non-Ohmic Behavior
- **Diodes:** They allow current to flow easily in one direction but restrict it in the opposite direction, showing a nonlinear I-V characteristic.
- **Transistors:** The current flow through a transistor depends on multiple factors, including the base-emitter voltage in a BJT or the gate voltage in a MOSFET.
- **Filament Lamps:** As the filament heats up, its resistance increases, resulting in a non-linear relationship between voltage and current.
In summary, non-ohmic conductors deviate from Ohm's Law because their resistance changes with factors like voltage, current, temperature, and material properties. This results in a nonlinear relationship between voltage and current, unlike ohmic conductors where resistance remains constant over a range of applied voltages and currents.