Temperature Dependence of Resistance.pptx

Describe the ability of a material to conduct current in terms of resistivity and conductivity

1. Effect of Temperature on Resistance & Resistivity

2. Today’s Focus Describe the effect of temperature increase on the resistance of a metallic conductor.

3. Resistance - is the characteristic that hinders the movement of electrons, particularly the flow of electric current. It's determined by the relationship between voltage and the electric current introduced into an electronic device Resistivity - is the phenomenon of specific electrical resistance of a material or volume resistivity of a material. It can also be defined as the intrinsic property of a material that displays how the material resists the flow of current in the material. The concept can also be defined as the resistance that is displayed by a conductor which has unit length and unit area of the given cross-section

4. Temperature Dependence of Resistance With increase in temperature of conductor, the number of collisions between the free electrons increases due to increase in thermal energy resulting in the random motion of electrons. These electrons find it difficult to drift in a particular direction for conduction. Hence the resistance of conductor increases as the temperature increases. When you increase the temperature, a semiconductor's, conductivity generally increases. This happens because the outermost electrons gain more energy and can leave the atom's shell. Conductors Semiconductors

5. Where (α) is called the temperature co-efficient of resistances. If the resistance of the material increases on increasing the temperature such materials have a positive temperature coefficient and when on increasing the temperature and the resistance decreases such materials have a negative temperature coefficient.

6. Temperature Dependence of Resistivity The resistivity of a material is temperature-dependent. The temperature dependence of the resistivity is different for conductors, semiconductors, and insulators. Conductors: In conductors, when the temperature goes up, the atoms begin to vibrate more vigorously. This increased vibration results in collisions between free electrons and other electrons. These collisions lead to a loss of energy from the free electrons, which are the ones responsible for carrying the electric current. As a result, the speed at which these electrons move, known as drift velocity, decreases due to this energy loss. This decrease in drift velocity causes the resistance of conductors, especially metals, to increase. In essence, as temperature rises, the resistance of the metal also goes up, which means it has a positive temperature coefficient of resistance. When the temperature is high, the resistivity of the conductor increases, and its conductivity decreases.

7. Temperature Dependence of Resistivity The resistivity of a material is temperature-dependent. The temperature dependence of the resistivity is different for conductors, semiconductors, and insulators. Insulators: • Insulators shift to the conduction zone with an increase in temperature. • The resistivity of an insulator decreases with temperature, resulting in an increase in conductivity. • Insulators exhibit a negative temperature coefficient of resistance.

8. Temperature Dependence of Resistivity The resistivity of a material is temperature-dependent. The temperature dependence of the resistivity is different for conductors, semiconductors, and insulators. Semi-conductors: • In semiconductors, as the temperature rises, the gap between the conduction band and the valence band narrows. This increase in temperature provides the valence electrons in the semiconductor with enough energy to break free from their covalent bonds and move up to the conduction band. • This , in turn, results in a greater number of charge carriers within the semiconductor at higher temperatures. The increased presence of these charge carriers lowers the resistance of the semiconductor. • Consequently , as temperature increases, the semiconductor's resistance decreases, making it more conductive. Thus, at high temperatures, semiconductors display excellent conductivity.

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