Current, Voltage and Resistance

Electric current is the flow of charge through a conductor.

The Three Quantities

Think of water in a pipe:

• Current (I) — the rate of charge flow, measured in amperes (A).
• Voltage (V) — the energy given to each unit of charge, in volts (V).
• Resistance (R) — opposition to current, in ohms (Ω).

Ohm's Law

V = I × R. Rearranged: I = V ÷ R and R = V ÷ I. This holds when temperature stays constant.

Series and Parallel

In a series circuit there is one path: current is the same everywhere and voltages add. In a parallel circuit there are branches: voltage is the same across each branch and currents add.

Practice

1. A 6 V supply drives 2 A. Find the resistance.
2. Explain why household appliances are connected in parallel.
3. Calculate the power of a 240 V appliance drawing 0.5 A.

Recap

Current is charge flow, voltage supplies energy and resistance opposes it. V = I × R ties them together.