Recall and use a simple electron model to explain the difference between electrical conductors and insulators and give typical examples

Published by Patrick Mutisya · 14 days ago

IGCSE Physics 0625 – Electric Charge

4.2.1 Electric Charge

Learning Objective

Recall and use a simple electron model to explain the difference between electrical conductors and insulators and give typical examples.

Key Concepts

Atoms consist of a nucleus containing protons (+) and neutrons (0) surrounded by electrons (–). The electron carries a fundamental charge

\$e = 1.6 \times 10^{-19}\,\text{C}\$

In the simple electron model, electric current is the flow of electrons through a material.

Conductors

In conductors, electrons are loosely bound to atoms and can move freely under an applied electric field.

  • Metals (copper, aluminium, silver, gold, steel)

  • Water containing dissolved salts (e.g., sea water)

  • Graphite

Insulators

In insulators, electrons are tightly bound to their atoms and cannot move freely.

  • Rubber

  • Glass

  • Plastic (e.g., P \cdot C)

  • Dry wood

  • Porcelain

Comparison Table

PropertyConductorsInsulators
Electron mobilityHigh – electrons move freelyVery low – electrons are bound
Typical examplesMetals, salty water, graphiteRubber, glass, plastic, dry wood
Use in circuitsWires, busbars, contactsCoatings, protective casings, handles
Resistance (Ω·m)\overline{10}⁻⁸ to 10⁻⁶\overline{10}⁸ to 10¹⁴

Explanation Using the Electron Model

  1. Apply a potential difference across a material.

  2. In a conductor, the electric field exerts a force \$F = eE\$ on free electrons, causing them to drift opposite to the field direction, producing a current \$I = nqAv_d\$.

  3. In an insulator, electrons are not free; the same field does not produce a measurable drift, so the current is negligible.

Suggested diagram: Illustration of free electron movement in a metal wire (conductors) versus tightly bound electrons in a rubber rod (insulators) when a voltage is applied.

Typical Exam Questions

  1. State two examples of good electrical conductors and two examples of good insulators.

  2. Explain why metal wires are used to connect components in a circuit but plastic is used for the outer covering of cables.

  3. Using the simple electron model, describe what happens to electrons when a battery is connected across a copper wire.

Summary

Conductors have many free electrons that can move easily, giving them low resistance and allowing electric current to flow. Insulators have electrons tightly bound to atoms, resulting in high resistance and preventing current flow. Understanding these properties helps in selecting appropriate materials for different parts of an electrical system.