3.4 Temperature effects on resistance
3 min read•august 6, 2024
Temperature affects resistance in materials, changing how they conduct electricity. This relationship is crucial for understanding electrical systems and device behavior under varying conditions.
Resistance can increase or decrease with temperature, depending on the material. Metals typically show when heated, while often exhibit . This knowledge is vital for designing and troubleshooting electrical circuits.
Temperature Coefficients
Impact of Temperature on Resistance
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- Temperature has a significant effect on the of materials
- As temperature changes, the resistance of a material can increase or decrease depending on its temperature coefficient
- Temperature coefficient of resistance quantifies how much the resistance changes per degree of temperature change
- Represented by the Greek letter alpha () and typically expressed in units of or \frac{%}{°C}
Types of Temperature Coefficients
- materials exhibit an increase in resistance as temperature rises
- Common PTC materials include metals like copper and aluminum
- materials display a decrease in resistance with increasing temperature
- Semiconductors and certain ceramics often have NTC behavior
- Material-specific behavior determines whether a substance has a PTC or NTC and the magnitude of the change
Calculating Resistance Change
- The change in resistance due to temperature can be calculated using the formula:
- represents the resistance at the new temperature
- is the initial resistance at the reference temperature
- is the temperature coefficient of resistance for the specific material
- Example: A copper wire with and at will have a resistance of at
Temperature-Sensitive Devices
Thermistors
- are temperature-sensitive resistors that exploit the NTC behavior of certain semiconductor materials
- As temperature increases, the resistance of a thermistor decreases significantly
- Thermistors are commonly used in temperature measurement, control systems, and thermal protection circuits
- Examples of thermistor applications include in home appliances, automotive temperature monitoring, and industrial process control
Linear Approximation
- For small temperature ranges, the resistance-temperature relationship of a thermistor can be approximated as linear
- The linear approximation simplifies calculations and allows for easier integration into control systems
- The linear approximation formula is given by:
- is the temperature coefficient of the thermistor, typically expressed in or \frac{%}{°C}
- The linear approximation is valid for temperature changes of around to from the reference temperature
Reference Temperature and Resistance
- Thermistor specifications often include a reference temperature () and the corresponding resistance at that temperature ()
- Common reference temperatures are and
- The reference resistance is used as a baseline for calculating the resistance at other temperatures
- Example: A thermistor with , at will have an approximate resistance of at using the linear approximation
Key Terms to Review (21)
Conductors: Conductors are materials that allow the flow of electric current with minimal resistance. This property is crucial in various applications, from basic electrical circuits to complex power systems, as it influences how energy is transmitted and utilized. The effectiveness of a conductor is influenced by its material properties, temperature, and the design of the system in which it is used.
Decreased Resistance: Decreased resistance refers to a reduction in the opposition that a material or component offers to the flow of electric current. This phenomenon is closely linked to temperature changes, as increased temperatures typically lead to increased atomic vibrations within conductive materials, allowing electrons to move more freely and reducing resistance.
Electrical Resistance: Electrical resistance is the measure of the opposition to the flow of electric current in a circuit, determined by the material's properties and physical dimensions. It is influenced by factors such as temperature, length, and cross-sectional area of the conductor, playing a critical role in how circuits behave under varying conditions. Understanding electrical resistance helps in predicting how components will perform and interact within electrical systems.
Electron mobility: Electron mobility refers to the ability of electrons to move through a material when an electric field is applied. It is a key factor in determining the electrical conductivity of materials, as higher mobility means that electrons can travel more freely, resulting in lower resistance. Understanding electron mobility helps explain how temperature variations can influence the behavior of materials, especially semiconductors and conductors.
Increased Resistance: Increased resistance refers to a rise in the opposition to the flow of electric current through a conductor, often influenced by various external factors. One of the primary factors affecting resistance is temperature; as temperature rises, the atoms in a conductor vibrate more, leading to more collisions between electrons and atoms, which increases resistance. This phenomenon is crucial in understanding how electrical devices operate under different thermal conditions.
Increased Thermal Energy: Increased thermal energy refers to the rise in kinetic energy of the particles within a material due to temperature changes. As the temperature increases, particles move more vigorously, leading to a change in physical properties such as resistance in electrical devices. Understanding this concept is crucial for grasping how temperature affects the performance and efficiency of electronic components.
Insulators: Insulators are materials that impede the flow of electric current due to their high resistance. They are crucial in electrical systems, as they prevent unwanted current leakage, ensuring safety and efficiency in electrical circuits and devices. Understanding insulators helps in grasping fundamental principles of electricity and the effects of temperature on resistance.
Joule Heating: Joule heating, also known as resistive or ohmic heating, is the process by which electrical energy is converted into heat energy when an electric current passes through a conductor. This phenomenon occurs due to the resistance within the material, causing energy to dissipate in the form of heat. As temperature rises, the resistance of most conductors also increases, which can lead to further heating and potential overheating of devices.
Kelvin: Kelvin is the SI unit of temperature, symbolized as 'K', and is a fundamental measure of thermal energy. It is the only temperature scale that begins at absolute zero, the point where molecular motion stops, and it is essential for scientific calculations involving temperature, particularly in physics and engineering. The Kelvin scale directly relates to other temperature scales like Celsius and Fahrenheit, making it crucial for converting and understanding temperature in various scientific contexts.
Negative Temperature Coefficient (NTC): A negative temperature coefficient (NTC) refers to a type of thermistor whose resistance decreases as the temperature increases. This property makes NTC thermistors valuable in temperature sensing and control applications, allowing them to provide accurate temperature measurements by correlating resistance changes to temperature variations. Understanding NTC behavior is crucial when considering the effects of temperature on resistance in electronic components.
Ohm: An ohm is the unit of measurement for electrical resistance in a circuit. It quantifies how much a material resists the flow of electric current, establishing a relationship between voltage, current, and resistance as expressed by Ohm's Law. Understanding ohms is crucial when looking at how different materials conduct electricity, how temperature impacts resistance, and how components interact in various circuit configurations.
Positive Temperature Coefficient (PTC): A positive temperature coefficient (PTC) is a property of certain materials where their electrical resistance increases with an increase in temperature. This characteristic is significant because it can lead to self-regulation in devices, preventing overheating by limiting current flow as temperatures rise. PTC materials are commonly used in applications like circuit protection and temperature sensors.
R(t) = r0[1 + α(t - t0)]: The equation r(t) = r0[1 + α(t - t0)] describes how the resistance of a material changes with temperature over time. In this equation, 'r(t)' represents the resistance at a given temperature 't', 'r0' is the initial resistance at a reference temperature 't0', and 'α' is the temperature coefficient of resistance. This relationship is crucial for understanding how temperature affects the performance of electrical devices, which is essential in electrical engineering.
Resistive Heating: Resistive heating is the process by which electrical energy is converted into heat as electric current flows through a resistor. This phenomenon occurs due to the collisions between moving electrons and atoms in the material, leading to an increase in thermal energy. The amount of heat generated is influenced by the resistance of the material and the square of the current flowing through it, highlighting the interplay between electrical resistance and temperature effects.
Semiconductors: Semiconductors are materials that have electrical conductivity between that of conductors and insulators. They are essential in the development of electronic devices, as their ability to control the flow of electric current makes them key components in transistors, diodes, and integrated circuits. Understanding semiconductors is fundamental to grasping how electronic devices operate, including their applications in various fields and how their properties change with temperature.
Superconductivity: Superconductivity is a phenomenon where certain materials exhibit zero electrical resistance and the expulsion of magnetic fields when cooled below a characteristic critical temperature. This allows electric current to flow without energy loss, making superconductors highly valuable for various applications like magnetic levitation and powerful electromagnets. The behavior of superconductors is highly sensitive to temperature, which plays a crucial role in determining their effectiveness and usability.
Temperature Sensors: Temperature sensors are devices used to measure the temperature of an object or environment and convert that measurement into a signal that can be read and interpreted. These sensors play a critical role in many applications, including industrial processes, environmental monitoring, and consumer electronics, where precise temperature control is essential. Understanding how temperature affects resistance is vital for accurately using these sensors, as many operate on the principle that electrical resistance changes with temperature.
Thermal agitation: Thermal agitation refers to the random motion of particles in a material due to thermal energy, which increases with temperature. As temperature rises, the kinetic energy of the particles increases, leading to greater movement and, consequently, more collisions among them. This phenomenon has a direct impact on electrical resistance in materials, as the increased motion can affect how easily electrons can move through a conductor.
Thermistors: Thermistors are temperature-sensitive resistors that exhibit a significant change in resistance with changes in temperature. They are primarily used in temperature sensing and control applications, playing a crucial role in various electronic devices and systems. Their ability to provide accurate temperature readings makes them essential components in circuits designed for monitoring and regulating thermal conditions.
α: In the context of temperature effects on resistance, α (alpha) is the temperature coefficient of resistance. It quantifies how much a material's electrical resistance changes with temperature, typically expressed in units of ohms per degree Celsius (Ω/°C). Understanding α is crucial for predicting how resistive components will behave under varying thermal conditions, which is essential for ensuring stability and accuracy in electrical systems.
β: In the context of temperature effects on resistance, β is a coefficient that quantifies how the resistance of a material changes with temperature. It is essential for understanding how resistive components behave in different thermal environments, allowing engineers to predict performance and reliability in various applications. The β value is particularly significant for materials like semiconductors and thermistors, where resistance can vary significantly with temperature changes.