What happens to resistor as temperature increases?
2 Answers
When the temperature of a resistor increases, several changes occur depending on the type of material the resistor is made of. In general, the effect of temperature on a resistor can be understood by considering the material's **temperature coefficient of resistance (TCR)**, which defines how much the resistance changes with temperature. Here’s a detailed explanation of the key effects:
### 1. **For Typical Conductive Resistors (Metallic Resistors)**
Most resistors, particularly those made from metals, exhibit **positive temperature coefficients of resistance (PTC)**. This means that as the temperature increases, their resistance increases. The reason for this lies in the behavior of electrons in the metal:
- **Increased Atomic Vibrations:** As temperature rises, the atoms in the metallic structure vibrate more intensely.
- **Increased Electron Scattering:** These atomic vibrations cause more frequent collisions between electrons and atoms, making it harder for electrons to move through the material. This increased scattering leads to **higher resistance**.
Mathematically, this is expressed as:
\[
R_T = R_0 (1 + \alpha (T - T_0))
\]
Where:
- \(R_T\) is the resistance at temperature \(T\),
- \(R_0\) is the resistance at a reference temperature (usually room temperature),
- \(\alpha\) is the temperature coefficient of resistance,
- \(T - T_0\) is the change in temperature.
So, for metals, **resistance increases with temperature**.
### 2. **For Semiconductors and Thermistors**
Semiconductors and some types of resistors like **thermistors** (temperature-sensitive resistors) behave differently.
#### **Negative Temperature Coefficient (NTC) Resistors**
- Certain resistors, particularly **NTC thermistors**, have a **negative temperature coefficient**. This means that as the temperature increases, their resistance decreases.
In NTC materials (like carbon or ceramic-based resistors):
- **More Charge Carriers**: As temperature rises, more electrons gain enough energy to move from the valence band to the conduction band. This increases the number of charge carriers (electrons and holes), which lowers the resistance.
- **Applications**: NTC thermistors are commonly used for temperature sensing, as their resistance drops predictably with rising temperature, allowing circuits to detect or measure temperature changes accurately.
#### **Positive Temperature Coefficient (PTC) Resistors**
- **PTC thermistors** are designed to increase their resistance sharply at a certain threshold temperature. These are often used for overcurrent protection because when the current (and thus heat) increases too much, the resistance increases, limiting the current flow.
### 3. **For Carbon Composition Resistors**
- **Carbon resistors** generally have a small **negative temperature coefficient**. As temperature increases, the resistance tends to decrease slightly, but the effect is not as pronounced as in semiconductors.
### Summary: Effects on Resistors with Temperature Increase
- **Metallic resistors (e.g., copper, aluminum)**: Resistance increases with temperature due to increased electron scattering.
- **NTC thermistors (e.g., semiconductors, carbon)**: Resistance decreases with temperature because more charge carriers become available.
- **PTC thermistors**: Resistance increases sharply above a certain temperature threshold.
Thus, the temperature effect on resistance depends heavily on the material used in the resistor, and different types of resistors are designed to exploit these effects for specific applications.
### 1. **For Typical Conductive Resistors (Metallic Resistors)**
Most resistors, particularly those made from metals, exhibit **positive temperature coefficients of resistance (PTC)**. This means that as the temperature increases, their resistance increases. The reason for this lies in the behavior of electrons in the metal:
- **Increased Atomic Vibrations:** As temperature rises, the atoms in the metallic structure vibrate more intensely.
- **Increased Electron Scattering:** These atomic vibrations cause more frequent collisions between electrons and atoms, making it harder for electrons to move through the material. This increased scattering leads to **higher resistance**.
Mathematically, this is expressed as:
\[
R_T = R_0 (1 + \alpha (T - T_0))
\]
Where:
- \(R_T\) is the resistance at temperature \(T\),
- \(R_0\) is the resistance at a reference temperature (usually room temperature),
- \(\alpha\) is the temperature coefficient of resistance,
- \(T - T_0\) is the change in temperature.
So, for metals, **resistance increases with temperature**.
### 2. **For Semiconductors and Thermistors**
Semiconductors and some types of resistors like **thermistors** (temperature-sensitive resistors) behave differently.
#### **Negative Temperature Coefficient (NTC) Resistors**
- Certain resistors, particularly **NTC thermistors**, have a **negative temperature coefficient**. This means that as the temperature increases, their resistance decreases.
In NTC materials (like carbon or ceramic-based resistors):
- **More Charge Carriers**: As temperature rises, more electrons gain enough energy to move from the valence band to the conduction band. This increases the number of charge carriers (electrons and holes), which lowers the resistance.
- **Applications**: NTC thermistors are commonly used for temperature sensing, as their resistance drops predictably with rising temperature, allowing circuits to detect or measure temperature changes accurately.
#### **Positive Temperature Coefficient (PTC) Resistors**
- **PTC thermistors** are designed to increase their resistance sharply at a certain threshold temperature. These are often used for overcurrent protection because when the current (and thus heat) increases too much, the resistance increases, limiting the current flow.
### 3. **For Carbon Composition Resistors**
- **Carbon resistors** generally have a small **negative temperature coefficient**. As temperature increases, the resistance tends to decrease slightly, but the effect is not as pronounced as in semiconductors.
### Summary: Effects on Resistors with Temperature Increase
- **Metallic resistors (e.g., copper, aluminum)**: Resistance increases with temperature due to increased electron scattering.
- **NTC thermistors (e.g., semiconductors, carbon)**: Resistance decreases with temperature because more charge carriers become available.
- **PTC thermistors**: Resistance increases sharply above a certain temperature threshold.
Thus, the temperature effect on resistance depends heavily on the material used in the resistor, and different types of resistors are designed to exploit these effects for specific applications.
As the temperature of a resistor increases, its electrical properties can change in several ways. Here's a detailed explanation of what typically happens:
### 1. **Resistance Change**
The most notable effect of temperature on a resistor is the change in its resistance. For most resistors, resistance increases with temperature. This is due to the behavior of the material from which the resistor is made:
- **Metals**: For metallic resistors (such as those made of copper or nickel), resistance typically increases with temperature. This is because, as the temperature rises, the metal atoms vibrate more vigorously. This increased atomic vibration causes more frequent collisions between the electrons (which carry the current) and the metal atoms, leading to higher resistance. The relationship between resistance and temperature for a metallic resistor can be expressed by the equation:
\[
R_T = R_0 \left[1 + \alpha (T - T_0)\right]
\]
where:
- \( R_T \) is the resistance at temperature \( T \),
- \( R_0 \) is the resistance at reference temperature \( T_0 \),
- \( \alpha \) is the temperature coefficient of resistance (TCR).
- **Semiconductors**: For semiconductors and some other materials, resistance can decrease with increasing temperature. This is because higher temperatures increase the number of charge carriers (electrons and holes) available to conduct electricity, thereby decreasing the resistance. The relationship for these materials can be quite different and is often more complex.
### 2. **Thermal Noise (Johnson-Nyquist Noise)**
As temperature increases, the thermal noise, also known as Johnson-Nyquist noise, in a resistor also increases. This type of noise is generated by the random motion of charge carriers (electrons) in the resistor material due to thermal agitation. The power of this noise is directly proportional to the temperature and can be calculated using the formula:
\[
V_{\text{noise}}^2 = 4k_B T R \Delta f
\]
where:
- \( V_{\text{noise}}^2 \) is the noise voltage squared,
- \( k_B \) is Boltzmann's constant,
- \( T \) is the absolute temperature in Kelvin,
- \( R \) is the resistance,
- \( \Delta f \) is the bandwidth over which the noise is measured.
### 3. **Potential for Thermal Drift**
In practical circuits, temperature-induced changes in resistance can lead to thermal drift, which can affect the accuracy and stability of electronic circuits. This is particularly significant in precision applications where resistors need to have a low temperature coefficient and high stability.
### 4. **Material-Specific Behavior**
Different resistor materials have different responses to temperature changes. For instance:
- **Carbon Composition Resistors**: These can have significant resistance changes with temperature, and their resistance often increases with temperature.
- **Metal Film Resistors**: These generally have a lower temperature coefficient of resistance compared to carbon resistors, meaning their resistance changes less with temperature.
- **Wirewound Resistors**: These often have a higher stability with temperature changes compared to carbon resistors but can still experience changes.
### 5. **Thermal Expansion**
Temperature changes can also affect the physical dimensions of the resistor. As temperature increases, the resistor may physically expand. This can influence resistance if the resistor’s construction is sensitive to physical dimensions, though this effect is usually less significant compared to the resistance-temperature relationship.
In summary, as temperature increases, most resistors will experience an increase in resistance due to increased atomic vibrations, leading to higher resistance. The exact change depends on the type of resistor and its material properties.
### 1. **Resistance Change**
The most notable effect of temperature on a resistor is the change in its resistance. For most resistors, resistance increases with temperature. This is due to the behavior of the material from which the resistor is made:
- **Metals**: For metallic resistors (such as those made of copper or nickel), resistance typically increases with temperature. This is because, as the temperature rises, the metal atoms vibrate more vigorously. This increased atomic vibration causes more frequent collisions between the electrons (which carry the current) and the metal atoms, leading to higher resistance. The relationship between resistance and temperature for a metallic resistor can be expressed by the equation:
\[
R_T = R_0 \left[1 + \alpha (T - T_0)\right]
\]
where:
- \( R_T \) is the resistance at temperature \( T \),
- \( R_0 \) is the resistance at reference temperature \( T_0 \),
- \( \alpha \) is the temperature coefficient of resistance (TCR).
- **Semiconductors**: For semiconductors and some other materials, resistance can decrease with increasing temperature. This is because higher temperatures increase the number of charge carriers (electrons and holes) available to conduct electricity, thereby decreasing the resistance. The relationship for these materials can be quite different and is often more complex.
### 2. **Thermal Noise (Johnson-Nyquist Noise)**
As temperature increases, the thermal noise, also known as Johnson-Nyquist noise, in a resistor also increases. This type of noise is generated by the random motion of charge carriers (electrons) in the resistor material due to thermal agitation. The power of this noise is directly proportional to the temperature and can be calculated using the formula:
\[
V_{\text{noise}}^2 = 4k_B T R \Delta f
\]
where:
- \( V_{\text{noise}}^2 \) is the noise voltage squared,
- \( k_B \) is Boltzmann's constant,
- \( T \) is the absolute temperature in Kelvin,
- \( R \) is the resistance,
- \( \Delta f \) is the bandwidth over which the noise is measured.
### 3. **Potential for Thermal Drift**
In practical circuits, temperature-induced changes in resistance can lead to thermal drift, which can affect the accuracy and stability of electronic circuits. This is particularly significant in precision applications where resistors need to have a low temperature coefficient and high stability.
### 4. **Material-Specific Behavior**
Different resistor materials have different responses to temperature changes. For instance:
- **Carbon Composition Resistors**: These can have significant resistance changes with temperature, and their resistance often increases with temperature.
- **Metal Film Resistors**: These generally have a lower temperature coefficient of resistance compared to carbon resistors, meaning their resistance changes less with temperature.
- **Wirewound Resistors**: These often have a higher stability with temperature changes compared to carbon resistors but can still experience changes.
### 5. **Thermal Expansion**
Temperature changes can also affect the physical dimensions of the resistor. As temperature increases, the resistor may physically expand. This can influence resistance if the resistor’s construction is sensitive to physical dimensions, though this effect is usually less significant compared to the resistance-temperature relationship.
In summary, as temperature increases, most resistors will experience an increase in resistance due to increased atomic vibrations, leading to higher resistance. The exact change depends on the type of resistor and its material properties.