Electric current is the rate of flow of electric charge.
- Symbol: I
- Unit: ampere (A)
- Formula: I = Q / t where Q is charge in coulombs (C) and t is time in seconds (s)
1 ampere means 1 coulomb of charge passes a point every second.
Conventional current vs electron flow. By convention, current is drawn flowing from the positive terminal to the negative terminal. Electrons actually move the opposite way. In all circuit diagrams, we use conventional current.
Types of current:
- DC (direct current): flows in one direction only (batteries, USB, Arduino).
- AC (alternating current): reverses direction periodically (mains supply, e.g. 230 V at 50 Hz).
Example 1.1. A charge of 12 C passes a point in 4 s. Find the current. I = Q / t = 12 / 4 = 3 A.