 Birds have no problem sitting undisturbed on the high voltage power transmission line or the distribution lines that you often see lining the road. This ability has nothing to do with them being birds, it's actually all about the connections that they are making, or as we will see more importantly the connections that they are not making. So let's look at how birds are able to sit on these wires without getting electrocuted. To begin with let's refresh your understanding of electric current. Electric current is the movement of electrons. Your television, mobile, refrigerator all have electrons moving across their wires giving rise to some current and making the device work. One thing that the electron needs in order to move is some motivation or more specifically a difference in electric potential. You can think of this as let's say there is a person pushing a big ball up this ramp and when this ball reaches the top, when it reaches the top it has gained some gravitational potential energy, it is at a higher potential compared to what it was at the ground and now when it is let go, the ball will start rolling down and come to a state of lower potential or lower gravitational potential energy. Similarly for electrons to move in a wire you need some potential difference across its two ends and the relationship between the potential difference, the amount of current that there is in the wire and the resistance is given by the Ohm's law. So if the resistance is very high the current would be less for some potential difference and similarly if the resistance is less the current then in that case would be very high. In transmission lines even though the wires are of copper, copper is a great conductor even then it has some resistance to them. So when the electrons are moving across the wire there will be some potential drop because there is a resistance in these wires as well even though that is very very less but still there is some resistance. Now let's bring back the bird sitting on the wire. There is a tiny section of wire between the bird's licks which will have some resistance to it and even the bird's body even the bird's body has a resistance to it. We can see the parallel circuit in the making right. So the question is won't there be some current passing through the bird's body and if yes then why is it not experiencing any shock? At this point why don't you pause the video and maybe take a go at this question. Why do you think the bird is not experiencing any shock whatsoever? We know that current follows the path of least resistance right. Whichever path offers less resistance electrons will tend to follow that path and it turns out that the resistance of the bird's body it is much higher. It is much higher than the resistance of this tiny section of the wire between a b between the two touching points. So current that is moving across the wire tends to follow the same path it tends to keep on moving along the wire not moving across the bird's body. Now one question that came to my mind when I was looking at this situation was how can it be that there is no current flowing through the bird there must be some current flowing through it right because there is a resistance between point a and b so that means there will be some potential drop potential of a will not be exactly same as the potential of b so why is it that no current flows through the bird and it turns out that there is some current there is some current that flows through the bird but it is incredibly tiny it is so small that the bird does not even experience it let's let's try and figure out the value of that current using Ohm's law we can say that the current passing through the bird's body is VAB divided by a resistance of the bird and VAB VAB is nothing but the current in the small section of the wire into RAB the resistance of that small section of wire and apart from this we know that our bird we know that our bird is incredibly higher than RAB now let's say that the value of I the current is 1000 amperes in this in this wire when a bird sits on it we can see a parallel circuit in front of us so there must be some change in the resistance which should change the current in this fire so to be able to get some sense of that change first let's try and find the net resistance of our bird and this small section of wire RAB if we do find the net resistance then maybe that could give us some sense of how much the current should change when we do that when we use the net resistance in a parallel circuit formula the net resistance comes out to be equal to this and maybe you can pause the video and see for yourself if you're getting if you're getting something like this here we can say that since our bird is a lot higher than RAB so we can neglect the addition of RAB to our bird because this is this is a great number this is much more than RAB so adding just a small number to a big number does not really change the big number by much so we can neglect we can neglect RAB from this and then we can cancel off our bird with our bird in a numerator and denominator so that that just leaves a net resistance as equal to RAB here we see that when a really high resistive load is attached to a smaller resistive load in a parallel format the net resistance is more or less the same it's the same as the tiny the tiny resistance it will be slightly less but the decrease will be so small that we can neglect it so if the net resistance is not changing even when the bird is sitting the current in the wire which was 1000 amperes to begin with we can still we can say that the current is still 1000 even though the current will increase slightly again the increase would be so less that for this calculation we can sort of ignore it so this tells us that there is not much change in the current we can still take the current as 1000 so VAB is 1000 into into RAB divided by our bird at this point we would need some data so that we could plug in our bird in RAB and figure out the current in the bird so let's let's do that quickly on an average our bird the resistance of a bird's body that is around 2000 ohms and again on an average the resistance of this entire wire the entire transmission wire per unit length this is 2 into 10 to the power minus 7 ohms per centimeter and we can say that the distance between the two legs this is 10 centimeters this could tell us the resistance of the tiny section wire that will be RAB this is equal to 2 into 10 to the power minus 7 into 10 because this is resistance per unit and we know for how many centimeters do we need the resistance of so we are multiplying that with 10 this gives us 2 into 10 to the power minus 6 ohms and now when we plug in this value this value and the value of the current in this equation we should get the current moving across the bird when we do that this comes out to be equal to 10 to the power minus 6 amperes or just one micro ampere this current is extremely small so current of 1 micro amperes is flowing across the bird's body it's so small that the bird doesn't experience anything over here we saw that VAB the value of VAB was extremely less the potential difference between the point A and B was so less that the amount of current moving through the bird's body is to the order of minus 6 amperes but what would happen if the value of VAB is not less what if this value was huge let's look at that situation now here the bird places one foot on one wire and the other on a wire next to it which could be at a different potential and it usually is and again using some data we can say that the difference in the potential of these two wires on an average it is somewhere around 10 kilo volts so VAB now VAB now this is A this right here is B VAB this becomes 10 to the power 4 volts and the current through the bird in this case which is equal to VAB divided by the resistance of bird this is now equal to 10 to the power 4 divided by 2 into 10 to the power 3 so this approximately comes out to be equal to 5 amperes and the current of this magnitude will definitely it will definitely result in a bird getting electrocuted so we see that the electrons do not choose to move along the brown wire they choose to go through the bird's body to the blue wire that is because a potential difference between A and B is incredibly high there's a lot of motivation for the electrons to choose the path of the bird's body and to the blue wire they are going across a huge potential drop they are going to an extremely low potential which is great that is what the electrons want but that's not so great for the bird because a bird will get electrocuted like this so that that brings a question how do workers how do workers repair live electrical wires without getting hurt they do this by using insulating materials in their clothing and equipment which blocks the flow of electrons all right so that is the entire story of birds sitting on wires it depends a lot on what connections are the birds making if both of the legs are on the same wire the potential across its two legs will be so less that there is almost microamperes current flowing through the bird's body and it experiences nothing but if a bird or a monkey or a squirrel if it touches the wire next to it if it touches two wires at one instant then there's a huge potential drop and the electrons passes through the birds or the animals body electrocuting it