Temperature Coefficient Of Resistance

The temperature coefficient of resistance, often known as the “alpha” () constant, represents the resistance reportedly per degree of temperature change. All substances have a specified resistance (around 20° C) and their resistance changes by a certain amount when temperature changes. This coefficient is positive for pure metals, indicating that resistance rises as temperature rises. This coefficient is negative for the elements silicon,  carbon, plus germanium, indicating that resistance reduces as temperature rises. The temperature coefficient of resistance for some metal alloys is very near to 0, implying that resistance changes very little with temperature changes.

Relation Between Temperature and Resistance

Consider a conductor with a resistance of R₀ at 0°C and a resistance of R_T at T°C. The relationship between temperature and R₀ and R_T resistances is roughly described by

RT = R0 [1+ α (T-T0)];

RT = R0 [1+ α (∆T)]

As a result of the aforementioned equation, it is obvious that the variation in resistance value of the any substance owing to temperature is primarily determined by three factors –

• The resistance value at a given temperature.
• The temperature is rising.
• The resistance coefficient at different temperatures.

Regardless of the type of material, the value might change. When the temperature of a metal rises, the electrons get more kinetic energy and consequently higher speed, allowing them to collide more frequently. We know that any substance’s resistivity is determined by

ρ = (m/n)q2 τ

As a result, the resistivity is proportional to the number of electric charges per unit volume n and the relaxation time between collisions. The average speed of the current carriers, i.e., the electrons, rises as the temperature rises, resulting in more collisions.

There are two basic reasons why material resistance is temperature-dependent.

The no. of collisions between charge carriers and atoms therein the material has one effect. As the temperature rises, so does the number of collisions. Thus it’s reasonable to expect a slight increase in resistance as the temperature rises.

Since some materials have a negative temperature coefficient, this may not always be the case. As the temperature rises, more charge carriers are discharged, resulting in decreased resistance. This effect is common in semiconductor materials, as one might assume.

While examining the resistant temperature dependence, its temperature coefficients of resistance are usually believed to follow a linear law. This is true for metals and several other materials at room temperature. Yet, it has been observed that the resistance effects caused by the no. of collisions are not necessarily constant, especially for these materials at very low temperatures. The resistivity has been demonstrated to be inversely proportional to the average free path among collisions, which means that as the temperature rises, the resistivity/resistance rises. Thermal vibration of the atoms limits this beyond about 15°K (i.e., at absolute zero), resulting in the linear zone we are accustomed to.

Effect of Temperature On-Resistance

The electrical resistance varies as the temperature rises and falls. The resistance increases as the temperature rises, although it can also decrease in some instances. The rate of variation in resistance caused by temperature change varies depending on the type of material, as detailed below.

Metal: Over a narrow temperature range, all purest metals’ resistance increases with time temperature. The ions are nearly stationary at low temperatures. The ions inside of the metal gain energy as the temperature rises, and they begin to oscillate around their mean positions. The electrons collide with the oscillating ions. As a result, resistance rises as the temperature rises.

Alloy: Almost everything alloys increase their resistance as temperature rises, but the rate of increase is slower than those of metals. The resistance of some alloys, including Manganin, Eureka, and Constantan, remains virtually unchanged throughout a wide temperature range. The alloy is utilized to make the resistance box because of this feature.

Insulator, Semiconductor, and Electrolyte Resistance: As the temperature rises, the resistance of semiconductors, insulators, and electrolytes (silicon, glass, varnish, and so on) decreases.

At 0 degrees Celsius, the semiconductor is a good insulator. Some electrons gain energy and become available for conduction when the temperature rises. As a result, conductivity rises, and resistance falls as the temperature rises.

Conclusion

Temperature affects the resistance and electrical resistivity of any materials. Electronic and electrical circuits are affected by changes in electrical resistance. It has the potential to cause profound alterations in some people. As a result, the temperature dependence of resistance is indeed a significant metric for many applications. The temperature coefficient is stated for materials due to its relevance, with the most often used materials becoming commonly accessible. Temperature coefficients of resistance charts for many popular materials used in the electronic and electrical industries can be found near the bottom.