# Creation of electric field inside a conductor

My book says that as soon as the two ends of a conducting wire touches the two terminals of a battery, it generates an electric field inside the conductor. Why?

• Imagine a pipe filled with water with both ends sealed. You tilt the pipe by a certain angle with respect to the horizon, nothing happens. Now you and your friend simultaneously unseal the pipe from both ends and water leaks out of the pipe. The same happens to the metal rod (water - electrons in metal; gravity - potential difference between the terminals; insulating material, say air, between the rod's ends and the battery terminals - sealing on the pipe's ends; electron current - water leaking down the pipe). – MsTais Sep 11 '18 at 17:33

There is an electric field between the battery terminals even before you connect the wire. For example, positive ions in the air will be attracted towards the battery's negative terminal (and repelled by the battery's positive terminal). Vice versa for negative ions. The mean magnitude of the electric field strength is given by $$E=\frac{\text{pd between terminals}}{\text{distance between terminals}}.$$
When you connect a wire across the terminals, there will be some redistribution of free electrons in the wire, resulting in an electric field in the wire, parallel to the axis of the wire, constant in magnitude all along it and directed from the positive terminal of the battery towards the negative. The magnitude of the field strength will be$$E=\frac{\text{pd between ends of wire}}{\text{length of wire}}.$$Free electrons will flow through the wire as a result.