The simple circuit
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The idea
You press the switch and the lamp lights up. You take off a wire and it goes out. Why? The lamp only gets current when the current can run in a circle: from the battery through the wire to the lamp and back to the battery.
What to remember
- Circuit
A circuit is a closed path for the electric current, from the power source through the devices and back again.
A simple circuit has three parts:
- the power source, for example a battery. It has two poles, plus and minus.
- the load, for example a lamp. It turns the current into light.
- the wires, that is, cables. They connect the parts.
The circuit is closed. The current can flow from the battery through the lamp and back, so the lamp lights up. Labels: 1 battery, 2 lamp, 3 wire.
Source: https://github.com/lernapps/elektrizitaet. Licence: CC0-1.0.Broken means dark
If the circuit is open at one place, no current flows anywhere. That can be a loose wire, an open switch or an unscrewed lamp. Then the lamp does not light up.
Example
The torch
A torch holds batteries, a lamp and a switch. When you press the switch, it closes the circuit. The current flows through the lamp and it lights up. When you switch off, the switch opens the circuit again.
Practice
Exercise
Solution
The circuit is broken, so no current can flow. right answer
A circuit must be completely closed. A single open place is enough and the current stops flowing everywhere.
The battery is empty at once.
A battery does not run down when the circuit is open. No current flows.
The lamp needs two batteries.
A lamp lights up with a single suitable battery when the circuit is closed.
Current only flows in a closed circuit. A loose wire opens the circuit at one place, and then the lamp goes out.
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Exercise
Solution
a power source, for example a battery right answer
The power source supplies the current for the whole circuit.
a load, for example a lamp right answer
The load does something with the current, here it makes light.
wires that connect everything right answer
Without wires there is no path on which the current can flow from part to part.
a water hose
A water hose carries water. A circuit needs wires made of metal, for example copper cables.
A power source, a load and wires together form a simple circuit.
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Exercise
Solution
Right answer: The statement is false.
If the circuit is open, no current flows at all. The lamp does not light up.
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