Which conductors do not obey Ohms law?
2 Answers
Ohm's Law states that the current \( I \) passing through a conductor between two points is directly proportional to the voltage \( V \) across the two points, and inversely proportional to the resistance \( R \), represented mathematically as:
\[
V = IR
\]
However, not all conductors obey Ohm's Law. Conductors that do not follow this relationship are called **non-ohmic conductors**. These materials or devices have a nonlinear relationship between current and voltage, meaning their resistance changes with the applied voltage or current. Some common examples of non-ohmic conductors include:
### 1. **Semiconductors**
- **Diodes and Transistors**: These are classic examples of non-ohmic devices. In a diode, current flows easily in one direction (forward bias) but is blocked in the other direction (reverse bias), and the current-voltage relationship is nonlinear. Transistors, used for amplification and switching, also have complex, nonlinear characteristics.
### 2. **Filament of Incandescent Lamps**
- As the current through a tungsten filament increases, the filament heats up, and its resistance increases. The rise in temperature changes the relationship between current and voltage, making the filament a non-ohmic conductor.
### 3. **Superconductors**
- At very low temperatures, certain materials become superconductors, exhibiting zero resistance to current. When in this state, the relationship between voltage and current is not defined by Ohm’s Law because no voltage is required to drive current through the superconductor.
### 4. **Gas Discharge Lamps**
- Devices like neon lamps or fluorescent tubes exhibit nonlinear behavior. In these lamps, the current doesn’t follow a simple proportional increase with voltage. Instead, once a certain voltage threshold is reached, current can surge quickly.
### 5. **Thermistors**
- Thermistors are temperature-sensitive resistors. There are two types: **NTC (Negative Temperature Coefficient)** and **PTC (Positive Temperature Coefficient)**. Their resistance changes significantly with temperature, leading to a nonlinear current-voltage relationship.
### 6. **Zener Diodes**
- Zener diodes behave non-ohmically because they exhibit a sharp breakdown voltage in reverse bias. Once this voltage is reached, current increases rapidly with only a small change in voltage.
### 7. **Vacuum Tubes and Cathode Ray Tubes**
- These older electronic components have nonlinear current-voltage characteristics due to the thermionic emission of electrons.
### 8. **Electrolytes and Ionic Solutions**
- Electrolytes (e.g., saltwater) have nonlinear relationships between voltage and current, especially when subject to electrolysis, because the resistance depends on the ion mobility, temperature, and concentration of ions.
### Why Non-Ohmic Behavior Occurs
Non-ohmic behavior arises when the material's properties, such as temperature, structure, or the physical nature of its charge carriers, change in response to applied voltage or current. These factors make the resistance variable, causing a nonlinear relationship between voltage and current.
In summary, non-ohmic conductors are those whose current-voltage relationship doesn't remain constant as per Ohm’s Law, usually due to changes in temperature, physical structure, or other intrinsic properties of the material or device.
\[
V = IR
\]
However, not all conductors obey Ohm's Law. Conductors that do not follow this relationship are called **non-ohmic conductors**. These materials or devices have a nonlinear relationship between current and voltage, meaning their resistance changes with the applied voltage or current. Some common examples of non-ohmic conductors include:
### 1. **Semiconductors**
- **Diodes and Transistors**: These are classic examples of non-ohmic devices. In a diode, current flows easily in one direction (forward bias) but is blocked in the other direction (reverse bias), and the current-voltage relationship is nonlinear. Transistors, used for amplification and switching, also have complex, nonlinear characteristics.
### 2. **Filament of Incandescent Lamps**
- As the current through a tungsten filament increases, the filament heats up, and its resistance increases. The rise in temperature changes the relationship between current and voltage, making the filament a non-ohmic conductor.
### 3. **Superconductors**
- At very low temperatures, certain materials become superconductors, exhibiting zero resistance to current. When in this state, the relationship between voltage and current is not defined by Ohm’s Law because no voltage is required to drive current through the superconductor.
### 4. **Gas Discharge Lamps**
- Devices like neon lamps or fluorescent tubes exhibit nonlinear behavior. In these lamps, the current doesn’t follow a simple proportional increase with voltage. Instead, once a certain voltage threshold is reached, current can surge quickly.
### 5. **Thermistors**
- Thermistors are temperature-sensitive resistors. There are two types: **NTC (Negative Temperature Coefficient)** and **PTC (Positive Temperature Coefficient)**. Their resistance changes significantly with temperature, leading to a nonlinear current-voltage relationship.
### 6. **Zener Diodes**
- Zener diodes behave non-ohmically because they exhibit a sharp breakdown voltage in reverse bias. Once this voltage is reached, current increases rapidly with only a small change in voltage.
### 7. **Vacuum Tubes and Cathode Ray Tubes**
- These older electronic components have nonlinear current-voltage characteristics due to the thermionic emission of electrons.
### 8. **Electrolytes and Ionic Solutions**
- Electrolytes (e.g., saltwater) have nonlinear relationships between voltage and current, especially when subject to electrolysis, because the resistance depends on the ion mobility, temperature, and concentration of ions.
### Why Non-Ohmic Behavior Occurs
Non-ohmic behavior arises when the material's properties, such as temperature, structure, or the physical nature of its charge carriers, change in response to applied voltage or current. These factors make the resistance variable, causing a nonlinear relationship between voltage and current.
In summary, non-ohmic conductors are those whose current-voltage relationship doesn't remain constant as per Ohm’s Law, usually due to changes in temperature, physical structure, or other intrinsic properties of the material or device.