Which law is under use in this phenomenon?

Case : Read the passage and answer the question(s).

Let us consider a straight conductor moving in a uniform and time-independent magnetic field. Figure shows a rectangular conductor PQRS in which the conductor PQ is free to move. The rod PQ is moved towards the left with a constant velocity v as shown in the figure. PQRS forms a closed circuit enclosing an area that changes as PQ moves. The length RQ = x and RS = l and the magnetic flux is Φ_B enclosed by the loop PQRS.