Understanding the relationship between temperature and electrical resistance is fundamental in physics and electrical engineering. Temperature significantly influences resistance. This phenomenon is crucial in designing and operating electronic devices and in various industrial applications.
The effect of a change in temperature leads to increased resistance of the conductor. The resistance of the conductor is proportional to the temperature. Thus, the increase in temperature increases conductor resistance. The resistivity of the conductor changes with temperature, and it causes an increase in resistance.
As we all know, the resistance of the conductor changes with a change in its physical dimension. Conductor resistance is proportional to the length and inversely proportional to the area. Thus, the resistance of a particular value has a certain wire length and diameter. However, even without a change in the physical dimensions of a conductor, the resistance of the conducting materials tends to increase with an increase in temperature. Contrary to this, the resistance of the insulating material and semiconductor decreases with increased temperature.
The effect of temperature on the resistance of the conductor is an increase in the resistance value with an increase in temperature. The resistance of the conductor is proportional to the temperature. The increase in temperature of the conductor increases its resistance. The resistivity of the conductor changes with temperature, and it causes an increase in resistance.
Basics of Electrical Resistance
Electrical resistance is a measure of how much a material opposes the flow of electric current. It is quantified in ohms (Ω) and is determined by the material’s properties, dimensions, and temperature. Ohm’s Law gives the fundamental equation for resistance (R):
Where V is the voltage across the material, and I is the current flowing through it.
Effect of Temperature on the Resistance of the Materials
The effect of temperature on resistance varies between different materials, primarily categorized as conductors, semiconductors, and insulators.
We will discuss the effect of the temperature on the resistance of the following types of materials.
- Conductor
- Insulator
- Semiconductor
Effect of temperature on resistance of the conductor
In conductive materials like metals, resistance increases with an increase in temperature. This behavior is due to the increased thermal agitation of atoms, which scatters the electrons more frequently, thus hindering their flow. Mathematically, this relationship can be expressed using the temperature coefficient of resistance (α):
The temperature coefficient of the resistance shows the change in the resistance with a change in the temperature. We use this property of conductors for temperature measurement. The following materials have almost linear resistance and temperature graphs. Therefore, the following materials are most suitable for temperature measurement.
- Resistance temperature detector (RTD) -Pt-100, Cu-54
- Thermistor
Why Resistance Increases with Temperature
In a conductor with many free electrons flowing through it, the atoms’ vibrations lead to collisions between the free and captive electrons. Each collision absorbs energy from the free electron and causes resistance. The more the atoms jostle around in the material, the more collisions occur.
The reason for the change in resistance is the temperature, which depends on the current flowing in the circuit. The flow of current is the movement of electrons from one atom to another under the influence of an electric field. Electrons are very small, negatively charged particles that repel the negative electric charge and attract the positive electric charge. Therefore, under the application of electric potential, electrons migrate from atom to atom and finally toward the positive terminal.
Only some electrons are free to migrate. However, other electrons within each atom are held so tightly to their particular atom that even an electric field will not dislodge them. The current flowing in the material is, therefore, due to the movement of “free electrons,” and the number of free electrons within any material compared with those tightly bound to their atoms is what governs whether a material is a good conductor (many free electrons) or a good insulator (hardly any free electrons).
The effect of heat on the atomic structure of a material is to make the atoms vibrate, and the higher the temperature, the more violently the atoms vibrate. The vibration of the atom due to the collision of electrons produces heat. The collision hinders the path of electron flow, and thus, the resistance of the conductor increases with an increase in the temperature.
Effect of Temperature on Resistance of Insulator
In an insulator, however, there is a slightly different situation. There are so few free electrons that hardly can cause current to flow through them. Almost all the electrons are tightly bound to the nucleus of the atom. It is very difficult to break the bond at a normal temperature. Heating insulating material vibrates the atoms, and if heated sufficiently, the atoms vibrate violently enough to shake some of their captive electrons free, creating free electrons to become carriers of current.
Thus, the free electrons reach from the valance band to the conduction band and cause the current to flow. Therefore, at a high temperature, an insulator’s resistance falls, and in some insulating materials, the resistance falls quite dramatically.
Thus, the resistance of the insulator decreases with an increase in temperature.
Effect of Temperature on Resistance of Semiconductor
In a semiconductor, the resistance decreases with an increase in temperature. The resistance of the semiconductor material decreases non-linearly with an increase in temperature. Thus, the semiconductor devices exhibit non-linear or non-ohmic characteristics.
The material is said to have a positive temperature coefficient if the resistance increases with an increase in temperature.
When resistance decreases with an increase in temperature, the material is said to have a negative temperature coefficient.
In general, conductors have a positive temperature coefficient, while insulators have a negative temperature coefficient (at high temperatures).
Different materials within either group have different temperature coefficients. Materials chosen for constructing the resistors used in electronic circuits have a very low positive temperature coefficient. In use, resistors made from such materials will have only very slight increases in resistivity. Therefore, the use of such materials for the manufacture of resistors creates components whose value changes only slightly over a given range of temperature. The resistance used as a heating element has a very low positive temperature coefficient.
Example:
The resistance of a platinum resistance thermometer at 0°C temperature is 2.75Ω and at 100 0°C it is 3.75Ω. Its resistance at an unknown temperature is 3.0Ω. Find the value of the unknown temperature.
Given Data
R0=2.75Ω
R100=3.75Ω
Rt= 3.0Ω
t=?
From R0 and R100 values, we will calculate the temperature coefficient of resistance(α).
Using the value of α, we can calculate the temperature at resistance 3.0 Ω.
The resistance of the platinum resistance thermometer is 3 Ω at 25 0°C.
Conclusion
The effect of temperature on resistance is a key concept in the design and operation of electronic systems. Conductors, semiconductors, and insulators exhibit distinct behaviors under varying temperatures. The resistance of the conductor increases with an increase in temperature, while the resistance of insulators and semiconductors decreases with an increase in temperature.
FAQs on the Effect of Temperature on Resistance
Q1. What is electrical resistance?
Electrical resistance is the measure of how much a material opposes the flow of electric current. It is quantified in ohms (Ω).
Q2. How does temperature affect the resistance of conductors?
In conductors, resistance typically increases with an increase in temperature. This is due to the increased thermal agitation of atoms, which scatters the electrons more frequently, thereby hindering their flow.
Q3. Why does the resistance of semiconductors decrease with an increase in temperature?
In semiconductors, an increase in temperature generates more charge carriers (electrons and holes), which enhances their conductivity and thus decreases their resistance.
Q4. How does temperature affect the resistance of insulators?
In insulators, resistance generally decreases with increasing temperature, but the change is not as pronounced as in semiconductors. The increased thermal energy allows some electrons to break free from their atomic bonds, contributing to a slight increase in conductivity.
Q5. Why is understanding the effect of temperature on resistance important in electrical engineering?
Understanding this effect is crucial for designing and operating electronic devices and systems. It helps in preventing overheating, ensuring efficient operation, and developing temperature-resilient technologies.
Q6. What is an example of a practical application that relies on the temperature dependence of resistance?
An example is the use of thermistors and resistance temperature detectors (RTDs) in digital thermometers, where the change in resistance with temperature is used to provide accurate temperature readings.
Q7. How do you calculate the change in resistance with temperature for a given material?
The change in resistance with temperature can be calculated using the formula:
where RT is the resistance at temperature T, R0 is the resistance at a reference temperature T0, and α is the temperature coefficient of resistance.
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