# Electric circuit

An electrical circuit is made up of components linked to each other by electric wires.

The objective is to transmit the energy contained in the movement of a large number of electric charges to a receiver.

This movement of electric charges is called an electrical current.

An electric current flows if at least one of the components of the network is a generator.

Furthermore, the circuit must form a closed path through which charge can flow and return to its starting point.

The opening and closing of the circuit can be controlled with a special component: the switch.

Disconnecting a conductor anywhere along the circuit has the same effect as opening the switch.

Circuits come in all sizes and shapes. The loop of the circuit can be only a few millimeters in the case of integrated circuits for example…

or several kilometers for the electrification of a train…

In every case, there is a path for the return of the current.

To standardize the representation of electric circuits, a symbol is associated to each element of the circuit.

Here is the standard diagram of the initial circuit.

Let’s imagine now that we want to connect a second light bulb.

We can put two light bulbs on the same branch.

Or we can put them on two separate branches.

In the first case, we say that the light bulbs have been connected in series.

They have one terminal in common and the current that flows through the first light bulb is the same as the one flowing through the second one.

If the filament in one of the light bulbs is broken, the current is blocked in the whole branch and the other light bulb is turned off.

In the second case, the light bulbs are set up in parallel. The charges can take two different paths and the current in each light bulb can be different. If one of the light bulbs is faulty, the other one continues to light up.

Lamps in a house, like trains on the same railway line, are connected in parallel.