Know that electric current is related to the flow of charge

What is Electric Current?

Electric current, denoted by the symbol I, is the flow of electric charge through a conductor. Think of it as a stream of tiny charged particles (mostly electrons) moving from one point to another.

Mathematically, it is defined as the amount of charge that passes a point in a circuit per unit time:

$I = \dfrac{dQ}{dt}$

Here, Q is the charge in coulombs (C) and t is time in seconds (s). The SI unit of current is the ampere (A), where 1 A = 1 C s⁻¹.

Analogy: Water Flow

Imagine a water pipe:

• Water = electric charge (electrons).
• Pipe = conductor (wire).
• Water flow rate = electric current.

Just as the amount of water that passes a point in a second is the flow rate, the amount of charge that passes a point in a second is the electric current.

Units and Measurement

Exam Tips 📚

• Remember the definition: I = dQ/dt – current is the rate of charge flow.
• When converting units, use the conversion factors (1 A = 1000 mA, 1 A = 1,000,000 µA).
• For word problems, draw a simple circuit diagram to keep track of where charge flows.
• Check that your answer has the correct unit (A, mA, µA).
• Use the water‑flow analogy to explain why increasing the number of electrons per second increases current.

Practice Question

A battery supplies a charge of 5 C in 10 s. What is the current produced?

1. Use the formula $I = \dfrac{Q}{t}$.
2. Substitute $Q = 5\,\text{C}$ and $t = 10\,\text{s}$.
3. Calculate $I = 0.5\,\text{A}$.

Answer: $0.5\,\text{A}$ (or 500 mA).