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The prerequisites for electric current are:
- Completeness of the circuit - The flow of electricity can be considered as a process in which electrons are drawn from the earth by a power plant. These electrons travel through electrical lines to our devices and travel all the way back to Earth. This circuit has to be completed for the current flow.
- Another possible factor determining the direction of flow of current is the (electric) potential. Current always flows from high potential to low capacitance. In other words, it can be said that electrons flow from lower potentials to higher ones. (The direction of electric current is opposite to that of electrons). Therefore we need a potential difference in current for the flow.
- The path of least resistance - In the case of a parallel path, the factor that flows the current into the current is presented by the (electrical) resistance path. The current will always flow in the path that provides the least resistance.
- Now consider that a bird is sitting on the living wire and is not touching any other wire:
- The first circuit is incomplete because the bird is not in contact with any other wire.
- There is no possible difference because both legs of the bird are touching the same wire at the same constant potential
- The resistance presented by the bird is also much higher than that presented by the copper/aluminium wire which are known to be good conductors of electricity hence there is an almost negligible amount of current flow through the bird which does not harm the bird.
- Indeed, when birds stand on a single-phase power line with both feet, they get electric shock in the nano volt range, making them feel nothing. Even though they do not complete a path on the ground, they are actually in parallel circuits with the power line.
- Since the electric line does not have 0 ohms of resistance, even between the legs of the bird, some electric current deviates into the bird. That is Ohm's law. Electricity will always follow all the given paths, but how much current flows through those paths depends on their resistance.
- If the bird touches the ground while sitting on the wire or flaps its wings and touches another electric wire with a different voltage, it will be shocked and likely to die from electrocution. This is because its body becomes a path for electricity to reach either a ground (any voltage) or a location with a different voltage (another wire at a different voltage).
