Charge
A fundamental property of matter that determines electrostatic and electromagnetic interactions. Charge is quantised: it comes in discrete units of elementary charge (e = 1.60 × 10⁻¹⁹ C). Two types exist: positive charge (protons, positive ions) and negative charge (electrons, negative ions). Like charges repel; opposite charges attract.
Formula
Q = ne
Real World
A lightning bolt transfers roughly 5 C of charge in milliseconds — equivalent to about 3 × 10¹⁹ electrons flowing from cloud to ground, each carrying the elementary charge of 1.60 × 10⁻¹⁹ C.
Exam Focus
When calculating numbers of electrons, divide total charge by e = 1.60 × 10⁻¹⁹ C — always show this substitution to earn the method mark.
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