Electricity: Circuits, Current, and Control

You flick a switch and a room floods with light — but what is actually happening in that fraction of a second? Electricity is invisible, yet it powers almost everything around you: your phone, your school's heating, hospital life-support machines. Before diving in, think about what you already know. Have you ever built a simple circuit? Have you noticed that a torch goes dim when its batteries run low? These everyday observations are clues to the science you are about to explore.

**What is electric current?** Electric current is the flow of tiny, negatively charged particles called electrons through a conductor — usually a metal wire. Think of electrons like water molecules flowing through a pipe: the greater the flow, the stronger the current. Current is measured in amperes (A), often shortened to 'amps'. **Complete circuits** Current can only flow when there is a complete, unbroken loop called a circuit. If the loop is broken — for example, by an open switch — the flow stops immediately and the bulb goes out. Every component in the circuit must be connected in a continuous path from one terminal of the cell, through the external circuit, and back to the other terminal. **Key components and their roles** • **Cell (battery):** Provides the energy, called electromotive force (EMF), that pushes electrons around the circuit. More cells connected in series mean a higher voltage and more push. • **Bulb:** Converts electrical energy into light and heat. It contains a thin wire called a filament that resists the current and glows as a result. • **Switch:** Opens (breaks) or closes (completes) the circuit to control the flow of current. • **Resistor:** Opposes the flow of current. Resistance is measured in ohms (Ω). A higher resistance means a smaller current for the same voltage. **Voltage, current, and resistance — Ohm's Law** These three quantities are linked by one of science's most useful relationships: Voltage (V) = Current (A) × Resistance (Ω) If you increase the voltage (add more cells) but keep resistance the same, current increases — and the bulb glows more brightly. If you add more bulbs (increasing resistance) but keep voltage the same, current decreases and each bulb glows more dimly. **Series vs parallel circuits** In a series circuit, components are connected in a single loop. The current is the same through every component, but the voltage is shared among them. In a parallel circuit, each component has its own branch. Each branch receives the full voltage, so bulbs in parallel shine at full brightness — this is why household wiring is parallel.