High-voltage electricity is extremely destructive, so there are usually prominent warning signs on high-voltage towers or lines to remind people to stay away. However, many birds often rest on high-voltage lines. So why don’t birds get electrocuted when they stand on high voltage lines?
Resistance and Current
First of all, the premise of electrocution is to generate a certain amount of current, and to generate current is to have a complete circuit. Electrical resistance exists in all the common things in our daily lives. Birds and humans also have electrical resistance.
Electrical resistance is like an invisible wall that impedes the transmission of current. The greater the resistance, the greater the impediment to current flow. From Ohm’s law I=U/R, it can be concluded that in the case of a fixed voltage, the greater the resistance, the smaller the current generated.
Both the bird and the high-voltage line (línea de alto voltaje) have a resistance. However, since the high-voltage line is mainly used to transmit electrical energy, its resistance is reduced as much as possible. This allows the more current to pass through and reduces losses. So, the resistance of the high-voltage line can be regarded as approximately 0.
The bird is small and carries a small resistance on its body. However, compared with the high-voltage cable, even if the bird has only a little resistance, it appears to be very large in terms of current. Therefore, most of the current will choose the better way, which is to pass through the high voltage line. In fact, the high-voltage wire is also resistive, resulting in some current flow to the bird. But because it is too small, even the bird itself can not feel.
Another reason is that the bird is relying on two claws to stand on the high voltage line. If their claws are far apart, similar to a person’s legs, then a potential difference is created, which leads to electrocution.
The potential difference is similar to the size of the water pressure caused by the height of the water level. In the same container, the higher the water level, then the greater the water pressure. Similarly, the greater the potential difference, the greater the voltage generated. Because of the small size of the bird, so the distance between the two claws is quite close. Then there is almost no potential difference, which means, there is no voltage. The absence of potential difference is referred to as equipotential. Therefore, there is no current passing through the bird.
So there are two main reasons why a small bird standing on a high voltage line will not be electrocuted.
- The bird’s own resistance is greater than the resistance of the high-voltage line, so the current passes through the high voltage line.
- The distance between the two claws of a bird is very small. So, the bird and the cable are equipotential and no potential difference is formed.