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

4.2.1 Electric Charge

⚡️ Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric field.

The simplest model is the electron model where atoms consist of a nucleus (protons + neutrons) surrounded by electrons. Electrons carry a negative charge of magnitude \$e = 1.602\times10^{-19}\,\text{C}\$, while protons carry an equal and opposite positive charge.

When electrons can move freely, the material behaves as a conductor; when they are tightly bound, it behaves as an insulator.

Electron Model & Charge Quantisation

  • Atoms are neutral: \$N{\text{p}}e = N{\text{e}}e\$.

  • Charge is carried only by electrons (and protons). The smallest unit of charge is the electron charge \$e\$.

  • In a conductor, electrons are delocalised and can move under an electric field.

  • In an insulator, electrons are bound to atoms and cannot move freely.

Conductors vs. Insulators

PropertyConductorsInsulators
Free electronsMany (delocalised)Few (bound)
Electrical conductivityHighLow
Typical useWires, batteries, circuitsInsulation, plastic, rubber

Typical Examples

  1. ⚡️ Conductors: copper wire, aluminium foil, steel, silver.

  2. 🧱 Insulators: rubber gloves, plastic tubing, glass, wood.

  3. 🔌 Semiconductors (between the two): silicon, germanium – useful in electronics.

📌 Exam Tip: When asked to explain why a material is a conductor or insulator, start with the electron model – mention free vs. bound electrons, then link to conductivity. Use the comparison table to structure your answer clearly. Remember to give at least one example for each type.

🔍 Quick Check: If a material can carry an electric current easily, what can you say about its electrons?


Answer: It has many free (delocalised) electrons → it is a conductor.


If it resists current, its electrons are bound → it is an insulator.