Is Electric Charge Conserved?

Yes. Electric charge is conserved: the total charge of an isolated system remains constant, although charge may be transferred between objects. This is required at both SL and HL in D.2 Electric and magnetic fields.

The Reasoning

The law of conservation of electric charge states that electric charge cannot be created or destroyed. Therefore,

$$Q_{\text{initial}} = Q_{\text{final}}.$$

An object becomes charged because electrons move into or out of it, not because charge appears. Protons remain bound inside nuclei during ordinary electrostatic processes, while electrons can be transferred by friction, contact or electrostatic induction.

For example, suppose two initially neutral objects are rubbed together. If object A gains a charge of $-3.2 \times 10^{-8}\,\text{C}$, it has gained electrons. Object B must lose the same amount of negative charge and therefore acquire $+3.2 \times 10^{-8}\,\text{C}$. The total charge is still

$$Q_{\text{total}} = -3.2 \times 10^{-8} + 3.2 \times 10^{-8} = 0\,\text{C}.$$

A common misconception is that rubbing objects creates charge. It does not: rubbing transfers electrons that were already present. Charge is also quantized, so an object's net charge is an integer multiple of the elementary charge: $q = ne$.

Exam Technique

For a Calculate or Determine question, define the system and write $Q_{\text{initial}} = Q_{\text{final}}$ before substituting values. Include charge signs carefully, and remember that a negative charge indicates excess electrons, not a negative amount of charge.