Level 1: Why Birds on 11 kV Wires Don't Get Shocked
Put a number on the voltage between its feet.
A bird stands on an 11 kV power line with its feet 5 cm apart. The line carries a current of 200 A and its resistance is 0.4 Ω per km. The potential difference between the bird's feet is about:
Only the short piece of wire between the feet matters. Change the resistance per kilometre to per metre, then take 5 cm of it.
So the voltage across the bird is about 4 mV, a few thousandths of a volt. The 11 kV is the line's potential relative to the earth: the whole bird sits at that potential, and only the 4 mV between its feet can drive a current through it, far too little to feel. Forgetting that the 0.4 Ω is per kilometre gives 4 V.
Every Level 2 starts from a quick question, Level 1, and changes one thing. Seeing what that change does is the skill JEE Main tests. Try it here, free and with no signup, then read the worked answer.
