Question

Predict the effect (if any) of an increase in temperature on the electrical conductivity of (a) a conductor; (b) a semiconductor; (c) an insulator.

Short answer

For conductors, conductivity decreases with temperature. For semiconductors, conductivity increases. For insulators, conductivity slightly increases but remains very low.

Step-by-step solution

Understanding Electrical Conductivity

Electrical conductivity is the measure of a material's ability to conduct an electric current. It varies with changes in temperature depending on the type of material.

Effect on Conductors

For conductors (such as metals), as temperature increases, the electrical conductivity decreases. This is because the increased thermal energy causes more collisions between the free electrons and the metal ions, which impedes the flow of electrons.

Effect on Semiconductors

For semiconductors (such as silicon), an increase in temperature leads to an increase in electrical conductivity. Higher temperatures excite more electrons from the valence band to the conduction band, thereby increasing the number of charge carriers available to conduct electricity.

Effect on Insulators

Insulators have a very low conductivity at low temperatures. However, as temperature increases, there might be a marginal increase in conductivity because a few electrons may gain enough energy to cross the significant energy gap to participate in conduction. Nonetheless, they remain poor conductors.

Key concepts

Electrical Conductivity

Electrical conductivity measures how well a material can carry an electric current. It's influenced by the material's structure and the presence of charge carriers, like free electrons. Different materials react differently to temperature changes, affecting their ability to conduct electricity. Understanding these variations helps in predicting how materials perform in different environments.

Conductors

Conductors are materials, like metals, that allow electricity to pass through them easily. They have many free electrons that move and carry electric charges. When the temperature rises, these electrons collide more frequently with the metal ions because of increased thermal energy. This results in a decrease in electrical conductivity since more collisions hinder the flow of electrons. Hence, higher temperatures generally reduce the conductivity of conductors.

Semiconductors

Semiconductors, such as silicon, have electrical properties between those of conductors and insulators. Their conductivity improves with temperature increase. At higher temperatures, more electrons gain enough energy to jump from the valence band to the conduction band. This process increases the number of charge carriers, thus enhancing the material's ability to conduct electricity. Therefore, elevating the temperature boosts a semiconductor's electrical conductivity.

Insulators

Insulators are materials that resist the flow of electric current. Examples include rubber and glass. These materials have very few free electrons, creating a significant energy gap that restricts electron movement. As the temperature rises, some electrons may gain enough energy to cross the energy gap, but this increase in conductivity is minimal. Insulators typically remain poor conductors of electricity, regardless of temperature changes.