What Is an Electric Circuit?
Imagine a water park where water flows through pipes, slides, and pools in a continuous loop. An electric circuit works in a remarkably similar way — except instead of water, we have electric charge flowing through wires and components.
A closed, continuous pathway through which electric current can flow from an energy source, through one or more components, and back to the source.
For a circuit to work, three things are essential:
- An energy source — such as a battery or power supply — that provides the "push" to move charges
- A conducting pathway — usually metal wires — through which charges can travel
- A closed loop — the path must be unbroken; any gap stops the flow
Think of a circuit like a circular running track. Runners (charges) need a complete loop to keep moving. If someone digs a trench across the track (an open switch), no one can complete a lap. The coach shouting encouragement is like the battery — providing the energy that keeps everyone moving.
If any part of the circuit is broken — a wire is disconnected, a switch is open, or a bulb filament has snapped — current cannot flow. We call this an open circuit. When the path is complete and current flows, we have a closed circuit.
Electric Current: The Flow of Charge
The rate of flow of electric charge through a conductor, measured in amperes (A).
In metal wires, the charges that actually move are electrons — tiny negatively charged particles. When a battery is connected, it creates an electric field that pushes electrons through the wire.
Conventional current vs electron flow: Historically, scientists agreed that current flows from the positive terminal to the negative terminal of a battery. We now know electrons actually flow the opposite way — from negative to positive. In your MYP course, you'll usually use conventional current direction (positive to negative) unless told otherwise.
Current is measured using an ammeter, which is always connected in series — meaning the current must flow through the ammeter.
The symbol for current is , and the unit is the ampere (A).
- A typical LED might use about (20 milliamps)
- A household light bulb might use about
- An electric kettle might draw about
A common misconception is that current gets "used up" as it flows through a bulb or resistor. This is not true! The current entering a component is exactly the same as the current leaving it. What gets transferred is energy, not charge.
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