DefinitionQuestion 1 · Recall
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By the end you can explain what electric current is, distinguish conventional current from electron flow, and state that charge is quantised in multiples of the elementary charge e = 1.60 × 10⁻¹⁹ C.
Electric current is a flow of charge carriers. In a metal wire the charge carriers are electrons (negative). In an electrolyte (salt solution) they are ions (positive and negative). In a plasma or gas discharge they can be electrons and positive ions.
Current is the rate of flow of charge:
where is current in amperes (A), is charge in coulombs (C), and is time in seconds (s). 1 A = 1 C/s — one ampere means one coulomb of charge passes a point every second.
Electric current
The rate of flow of charge: . Unit: ampere (A), where 1 A = 1 C s⁻¹.
Before electrons were discovered, early scientists (Franklin, Ampere) arbitrarily defined current as flowing from positive to negative. By the time J.J. Thomson found the electron (1897), the convention was everywhere — textbooks, instruments, circuit diagrams. Changing it would have caused chaos, so we stuck with it.
Conventional current = direction a positive charge would move. Electron flow = direction electrons actually move (negative to positive).
In most circuits this makes no difference to the maths — just be consistent. The syllabus and exam questions use conventional current unless explicitly stated otherwise.