Using cylindrical co-ordinates (r, theta, z), calculate the electric flux phi=integral D . dS when the displacement vector D is given by: D=10ezcos(theta)/r2 . kr + z2sin(theta)/r2 . Kz and the surface S is part of a cylinder of radius a=0.3, defined by 0 is less than or equal to z which is less than or equal to 1 and 0 is less than equal to theta which is less than or equal to pi/4 I’ve put the equation in the cylindrical co-ordinates: (10ezcos(theta)/r2, 0, z2sin(theta)/r2) From there I’ve written out S as S(Sr, Stheta, Sz) I know that the perpendicular lines define the surface. In this case Sz is perpendicular which means than Sr is the main component. Then: D . DS = DrdSr + DthetadStheta + DzdSz But I don’t know where to go from here..... Any help?