Metal rod in an electric field A metallic rod is placed in a uniform electric field. 
Why is an electric field induced in the opposite direction?
 A: 
Let us start from the very basic intution ......a charge placed in a field experiences some force .the direction of the forces matches with the field if the charge is positive. Now we know that a conductor is a cluster of free electrons hence when placed in a field the charged particles experience a force that drift them in a direction opposite to the field hence developing an increased concentration of electrons on that side and a deficiency on the other causing  development of a potential difference between the two sides of the conductor giving rise to an electric field which grows in magnitude until net force experienced by every charge particle is zero
A: The electrons are free in a conductor, so in an external electric field they will start to move as the field prescribed them to. The movement of electrons will make the electrons density in the rod non-uniform, which will produce a net electric field which will gradually cancel the applied external electric field until the electrons feel no net force.
The field can be uniform, it will still produce an induced field.
