Purpose

Build a useful atomic model for electrical work without implying that current is simply electrons racing from source to load.

Learning objectives

• Identify proton, neutron, and electron charge
• Distinguish atomic structure from a circuit model
• Explain mobile charge carriers in metals
• Relate charge imbalance to electrical effects

Electrical behaviour begins with charge. The atomic model explains why some particles are bound and why outer electrons in metals can respond collectively to an electric field.

Core theory

A neutral atom contains equal total positive and negative charge. Protons are positively charged, electrons negatively charged, and neutrons have no net charge.

In a metallic conductor, some outer electrons occupy states that extend through the material. An applied electric field produces a small net drift superimposed on their thermal motion.

The field establishing circuit behaviour propagates through the circuit far faster than the individual electrons drift; the source transfers energy through the electromagnetic system.

Assumptions: Elementary charge magnitude is 1.602176634 × 10⁻¹⁹ C; No other charge transfer occurs.

1. Direction: Losing negative electrons leaves positive net charge.
2. Multiply: Q = n e = (2.0 × 10¹²)(1.602176634 × 10⁻¹⁹ C).
3. Round: Q = +3.2 × 10⁻⁷ C = +0.32 µC.

The body carries approximately +0.32 µC.

Reasonableness check: A macroscopic coulomb represents an enormous number of elementary charges, so trillions of electrons still produce less than one microcoulomb.

Knowledge check

Answer: The circuit electric field is established through the system much faster than individual electrons drift. Energy transfer is not explained by one electron travelling from the source to the lamp.

Practical exercise

Draw a neutral atom and a positively charged atom, then annotate what changed and what did not change in the nucleus.

Summary

• Charge is a property of particles
• Metals provide mobile carriers
• Field propagation and carrier drift are different