The Relationship Between Temperature and Resistance
Temperature plays a significant role in determining the resistance of a material. In general, resistance increases with temperature for most materials, including metals. This is because as the temperature rises, the atoms within the material vibrate more vigorously, increasing the likelihood of collisions with electrons, which carry the electric current. These collisions impede the flow of electrons, leading to higher resistance.
Different Materials, Different Behaviors
While the general trend is for resistance to increase with temperature, there are some exceptions:
- Semiconductors: Semiconductors exhibit the opposite behavior, with their resistance decreasing as temperature rises. This is because at higher temperatures, more electrons are excited into the conduction band, increasing the number of charge carriers available for current flow.
- Thermistors: Thermistors are specifically designed to exploit the temperature dependence of resistance. There are two types:
- Positive Temperature Coefficient (PTC) Thermistors: These thermistors increase resistance as temperature rises.
- Negative Temperature Coefficient (NTC) Thermistors: These thermistors decrease resistance as temperature rises.
Practical Implications
The temperature dependence of resistance has practical implications in various applications:
- Electrical Circuits: Temperature changes can affect the performance of electrical circuits, especially in environments with extreme temperatures. This is why components like resistors are often rated for their temperature coefficient.
- Temperature Sensors: Thermistors are widely used as temperature sensors in various applications, including automotive systems, medical devices, and household appliances.
- Overheating Protection: PTC thermistors are used in circuit protection systems to prevent overheating by increasing resistance and interrupting the current flow.
Examples
- Heating a Wire: When you heat a wire, its resistance increases, which can lead to a decrease in current flow. This is why overheating can damage electrical wires.
- Thermostat: A thermostat uses a bimetallic strip, which bends due to temperature changes, to control the heating or cooling system based on the resistance of the strip.
Conclusion
The relationship between temperature and resistance is a fundamental concept in electrical engineering. Understanding this relationship is crucial for designing and operating electrical systems effectively.
