we know that emf is induced in a rod is e=vbl. due to this induced emf ,ends of rod acts as positive or negative potential means act as imaginary cell,but how can we confirm that Which end is positive or negative.
let us start in easy manner....
1.Spread your right hand in direction of moving rod.
2.Curl your fingers in direction of magnetic field.
3.Now your thumb in which direction that end of rod will be positive and other end will be negative.
Feel the subject.