A thin copper rod AB of length l is rotating with constant angular velocity about an axis passing through the end A and perpendicular to the plane of page in a uniform magnetic field of induction B→ as shown in the figure. P and Q are two points on the rod such that AP=l4 and AQ=l2. If ‘V’ is the induced potential at a point on the rod, then VQ−VP/VB−VA  is