Electric charge Knowledge-Based Study

Study notes

1. What is Electric Charge?

   Electric charge is a fundamental intrinsic property of matter that governs how particles interact electrostatically. Matter is composed of atoms, which contain positively charged protons, negatively charged electrons, and electrically neutral neutrons.

   • Positive Charge: Carried by protons.
   • Negative Charge: Carried by electrons.
   • Neutral State: An object containing equal quantities of positive and negative charge has a net charge of zero.

   The standard SI unit of electric charge is the coulomb (C). In microscopic interactions, charges are often expressed in microcoulombs (μC) or nanocoulombs (nC).

   The Elementary Charge

   Electric charge is not continuous; it is quantized. This means that any observable net charge exists only in discrete packets that are integer multiples of the fundamental elementary charge, denoted by the symbol e.

   The magnitude of the elementary charge is:

   $e \approx 1.602 \times 10^{-19}\text{ C}$

   A proton carries a charge of $+e$, while an electron carries a charge of $-e$. Consequently, the net electric charge $q$ of any isolated body can be expressed mathematically as:

   $q = n \cdot e$

   where n is an integer ($n = 0, \pm 1, \pm 2, \dots$). An isolated free charge can never be a non-integer fraction of e.

   Fundamental Rules of Electrostatics

   Two foundational principles dictate how electric charges behave and interact:

   1. Law of Conservation of Electric Charge

   In any closed or isolated system, the total net electric charge remains strictly constant over time. While charges can be transferred from one object to another through processes such as friction, conduction, or induction, charge can neither be created nor destroyed.

   2. Electrostatic Interaction

   Charged bodies exert forces on one another across space:

   • Like charges repel: Two positive charges or two negative charges push away from each other.
   • Opposite charges attract: A positive charge and a negative charge pull toward each other.

   An electrically neutral object carries no net charge, but it can still experience an attractive force toward a charged object due to electrostatic polarization.