D.2 Electric and magnetic fields

Have you ever rubbed two balloons on your hair and tried to bring them together? They push apart. Hold a magnet near a compass and the needle snaps into alignment. These familiar phenomena are governed by electric and magnetic fields , invisible regions of influence that exert forces on charged particles and current-carrying conductors.

Understanding these fields is central to electromagnetism, one of the four fundamental forces of nature. In this subtopic, you will explore:

• The nature of electric charge and the forces between charges
• How electric fields are defined and represented
• The concept of electric potential
• An introduction to magnetic fields and their effects

Electric Charge: A fundamental property of matter that causes particles to experience a force in an electric field. Charge comes in two types: positive (associated with protons) and negative (associated with electrons). Measured in coulombs (C).

Like charges repel each other; opposite charges attract each other. This interaction is the electric force, and it acts even across empty space.

Electric charge obeys two fundamental rules:

1. Conservation of Charge
The total electric charge in a closed system is always constant. Charge cannot be created or destroyed , it can only be transferred from one object to another.

2. Quantization of Charge
Charge does not come in arbitrary amounts , it always exists as integer multiples of the elementary charge $e$:
$e=1.6\times 10^{-19}\mathrm{C}$
So a charge of $q=ne$, where $n$ is an integer.