Simple Circuits
Introduced| English |
|---|
| circuit/ˈsɜːkɪt/ |
| electromotive force/ɪˌlektrəʊˈməʊtɪv fɔːs/ |
One battery, one bulb, one loop — and light
- Connect a battery to a bulb with two wires and the bulb glows.
- Break either wire and the light dies at once — the loop must be complete.
- A circuit 电路 is a closed path that lets charge flow from a source and back.
- Learn to read this simple loop and every complex circuit becomes approachable.
The parts of a circuit
- A source (battery or cell) supplies the energy, its voltage the "push".
- Wires carry the current with almost no resistance.
- Components (bulbs, resistors) use the energy the current delivers.
- A switch opens or closes the loop, turning the current on or off.
A single loop
Build a simple series circuit and see the same current flow through each part.
For current to flow in a circuit, the loop must be:
A complete, closed loop is needed; any break stops the current.
What does a switch do in a circuit?
A switch opens (off) or closes (on) the circuit loop.
Select all parts of a basic circuit.
A basic circuit needs a source, wires and a component. A magnet is not required.
EMF: the battery's push
- A battery's electromotive force (EMF) 电动势 is the voltage it provides — the energy per unit charge.
- It "lifts" charge to a high potential, ready to flow round and deliver energy.
- The current is the same everywhere in a single unbranched loop.
- Energy is carried from the battery to the components and turned into light or heat.
The voltage a battery provides — its energy per unit charge — is called its ____.
The electromotive force (EMF) is the battery's energy per unit charge.
In a single unbranched loop, the current is the same at every point.
With one path, the same current flows through every component.
Reading a circuit diagram
- Circuits are drawn with standard symbols: lines for wires, a pair of bars for a cell.
- Trace the loop from the + terminal, through each component, back to the −.
- If the loop is unbroken, current flows; a gap (open switch) stops it.
- This shorthand lets us plan and analyse circuits on paper before building them.
A circuit only works if the loop is complete. A single break anywhere — a loose wire, an open switch, a burnt-out bulb in series — stops all the current, not just at that spot. In a single loop the current is the same at every point.
A bulb in a single-loop circuit burns out. What happens to the current elsewhere in the loop?
A break in the single loop stops all current, not just at the bulb.
A $6\ \text{V}$ battery is connected to a single bulb, and $2\ \text{A}$ flows.
- The current is $2\ \text{A}$ everywhere in the loop — the same leaving and returning to the battery.
- Open a switch anywhere and the current everywhere drops to zero.
A circuit is a complete loop that lets current flow from a source (with its EMF) through wires and components and back. Break the loop anywhere and all current stops. In a single unbranched loop, the current is the same at every point.