Resistivity of Various Materials

Materials can be grouped into conductors, semiconductors, and insulators according to increasing resistivity.

Conductors

• Conductors have very low resistivity.
• Metals such as copper and aluminium are good conductors.
• Typical resistivity of metals is about 10⁻⁸ to 10⁻⁶ Ω m.
• They allow electric current to pass easily.

Semiconductors

• Semiconductors have a resistivity higher than that of conductors but much lower than that of insulators.
• Examples include silicon and germanium.
• Their resistivity decreases when the temperature increases.
• Their resistivity can be controlled by adding suitable impurities, a process called doping.

Insulators

• Insulators have extremely high resistivity.
• Materials such as rubber, plastic, glass, and ceramic are insulators.
• Their resistivity may be about 10¹⁸ times greater than that of metals or even more.
• They do not allow current to flow easily.

Important trend

• In metals, resistivity generally increases with an increase in temperature.
• In semiconductors, resistivity decreases with an increase in temperature.

Cause:

This difference is very important in exams because students are often asked to compare conductors and semiconductors conceptually. It also explains why semiconductors are useful in electronic components.

• Copper is used in household wiring because it has low resistivity.
• Plastic covering on wires is used because it is an insulator.
• Silicon is used in chips and electronic circuits because its conductivity can be controlled.