A circuit must always have a generator, a receiver and a conductor wire. The rest of the elements are optional. To explain how an electric circuit works, we will use the example in the figure, with a battery as generator, and a light bulb as receiver.
1. Close the switch
The circuit starts working when it is closed, and the bulb is connected to the battery.
2. Electron flow
The electrons are pushed by the battery. They come out of one of the battery ends (the negative pole), pass through the wires, the switch, the fuse and the receiver and finish their journey at the other battery end (the positive pole). But this happens at a very high speed, practically all at once, which is why the light turns on instantly when the switch is closed. And throughout the wire there are electrons flowing or not flowing at the same time, depending on whether the switch is closed or open.
3. To stop or restore the flow of current...
Just press the switch.
4. The fuse
It works as a protection element to prevent the circuit components from being damaged in the event of an overload. If this were to occur, the fuse would break and interrupt the flow of current.
Image created by Ana Dapena Mora from CANVA CC-BY-SA elements
How are the electric circuits of our home appliances?
2
Let's look at the example of a hairdryer . A hairdryer is a plastic case that contains various electrical elements inside. To see them and find out how they work, click on the active areas or icons in the image.
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Elements to move the air
It consists of a very long, coiled cable to heat the air.
It activates the flow of current to the dryer. There may be several, with different positions to regulate the air intake and temperature.
Current enters and leaves the circuit through it.
When we plug in our hairdryer, we are connecting it to the generator in our circuit. The generator is many miles away from our homes, but our power outlets connect to it when we plug something, through the wiring in our home and the cables on the power lines. That generator cannot be as small as a battery. It has to be something much more powerful since it has to produce the energy for many homes, offices, factories... In the next topic we will find out how electrical energy is produced.
Hair dryer electric circuit. Ana Dapena Mora, based on CANVA elements.
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Comprenhension activity 1. Choose the right answer
Look at this circuit:
Audio:
a) close the switch yellow
b) push the push bottom and open the switch green
c) push the push button and close the switch yellow and green
Comprenhension activity 2. Choose the right answer
Observe this circuit:
Audio:
a) switch A: red and green. We need to close switch B to allow current to pass through the yellow lamp
b) switch B: none. That circuit would not be closed, as it would be connected only to one side of the battery
c) both switches: all of them
Extension. The electric panel and the electric circuits of our houses
2
The electrical circuits in a home are connected at a distribution board or electrical panel. This panel is usually located in the basement or on a wall. From the panel, electrical wires run through the house and connect to outlets, switches, and other electrical devices.
Click on the active areas or icons in the image to see what the different switches in the electrical panel are and what they are used for.
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ICP (Power Control Switch) turns off the installation when you exceed your contracted power. When the power goes out and this switch has tripped, it is most likely that you have too many electrical appliances running. Turn off some of them and turn the switch back on.
IG (General switch) . Protects the circuit from network overloads, preventing short circuits.
PIAS (Small Automatic Switches) . They are responsible for protecting each of the internal circuits, so that you can independently activate or deactivate lighting, appliances or rooms.
DIF (Differential switch). Used to disconnect the installation, for example in the event of a leak or current derivations to ground, interrupting the supply for safety reasons.
The cables that distribute the current throughout the house come out of the electrical panel. In homes there are usually 5 independent circuits that supply the light points, the general-use power outlets and the refrigerator, the stove and oven, the washing machine, dishwasher and heater (electric water heater) and the power outlets in the bathrooms, and auxiliary kitchen outlets.
Each independent circuit has its own PIA (small automatic switch) in the electrical panel, so that if there is a problem in one of the circuits, it does not affect the others. The conductors of each circuit start from its PIA and run through the house inside corrugated PVC tubes embedded in the wall.
Along the route, these cables branch out to feed each receiver (light points and sockets) in junction boxes. Junction boxes are plastic boxes where connections and splices of electrical cables are made.
In this model you can see how the current distribution to the different independent circuits from the panel would be, simplified. Note that three cables go to each element of the circuit. The current goes through one and returns through another. The third cable, the yellow and green one, is the ground connection. This cable allows the charge to be diverted to the ground through the place that is marked in the same colors under the electrical panel. The ground cable protects all your appliances, your home and people from electrical overloads.
Table with the elements of a circuit and their symbols. Wikimedia Commons has media related to: Pila , Ramon Vasconcellos Bulb , Pxhere CC- 0 Resistance , Willtron at Wikimedia Commons Engine , Elmek at Wikimedia Commons 04 , Timbre , Czech Republic at Wikipedia , CC-BY-SA 04 , Fuse André Karwath Aka at Wikimedia Commons , CC-BY- SA Cables, Michal Jarmoluk and Pixnio.com CC0 Voltmeter , Angeloleithold in Wikimedia Commons , CC-BY- SA Ammeter, ETSIT UPM Students in Wikimedia Commons , CC0 Switch , Vectorportal.com CC-BY, Switch in Wikipedia , CC - BY-SA 4.0 , Button, Pxhere , CC0 
