Electricity Basics: Circuits and Current

What is electricity?

Everything is made of atoms, and atoms contain tiny charged particles. The most important for electricity are electrons, which carry a negative charge. Electricity is what we get when these charges build up or flow.

When charges flow steadily, we call it current electricity — the kind that powers your home. When charges build up and stay put (like the spark when you touch a doorknob), we call it static electricity. This lesson is about current.

Current, voltage and resistance

Three quantities describe what is happening in a circuit:

• Current is the flow of charge. More flowing charge means more current. It is measured in amperes (A), or amps.
• Voltage is the push that drives the charge around. A battery provides voltage. It is measured in volts (V).
• Resistance is how much a material opposes the flow. It is measured in ohms (Ω).

A helpful picture is water in a pipe: voltage is the water pressure, current is the amount of water flowing, and resistance is a narrow section that slows the flow. Turn up the pressure (voltage) and more water (current) flows; pinch the pipe (raise resistance) and less flows.

Circuits: the complete loop

For current to flow, the charge needs a complete, unbroken loop called a circuit. A basic circuit needs:

• a power source (a battery or cell) to provide voltage,
• conducting wires to carry the charge,
• a component such as a bulb or motor that uses the energy, and
• often a switch to open and close the loop.

Open the switch and you create a gap — the loop is broken and current stops instantly. That is exactly how a light switch works.

Conductors and insulators

Materials are sorted by how easily charge moves through them:

• Conductors let charge flow easily because they have free electrons. Examples: copper, gold, aluminium, and other metals.
• Insulators block the flow of charge. Examples: rubber, plastic, glass, and wood.

This is why wires have a copper core (a conductor) wrapped in plastic (an insulator) — the plastic keeps the current safely inside the wire.

Series and parallel circuits

There are two main ways to connect components.

In a series circuit, everything is joined in a single loop, one after another. The same current flows through every component. The catch: if one bulb breaks, the loop is broken and all the bulbs go out — like old-fashioned fairy lights.

In a parallel circuit, each component sits on its own branch. The current splits between the branches. If one bulb breaks, the others stay lit because their loops are still complete. This is how the lights in your house are wired, so switching off one lamp does not darken the whole room.

Feature	Series	Parallel
Number of paths	One	Many
If one component fails	All stop	Others keep working
Current	Same everywhere	Splits between branches

Where the energy goes

A circuit transfers electrical energy from the battery to the components, which transform it into light, heat, sound, or movement. That is one example of energy changing form — explore more in the many forms of energy.

Try it yourself! 🧪

Build a safe, simple circuit (low-voltage only — never use mains electricity).

1. Gather a 1.5 V battery, a small bulb in a holder, two wires, and a switch (or just touch the wire to make and break the loop).
2. Connect the battery, switch, and bulb in one loop so the charge can flow all the way round.
3. Close the switch — the bulb lights. Open it — the bulb goes out. You have controlled the current!
4. Add a second bulb in series and notice both dim slightly. Then rewire them in parallel and see them both shine brightly and work independently.

You have just built and compared real series and parallel circuits.