var('x,y,z,theta,phi')
vfield = plot_vector_field3d((y,x,0),(x,-10,10),(y,-10,10),(z,-1,10),plot_points=[6,6,4],\
colors='blue',center_arrows=True)
r = (9*sin(phi)*cos(theta),9*sin(phi)*sin(theta),9*cos(phi))
surface = parametric_plot3d(r,(theta,0,2*pi),(phi,0,pi/2),color='green',opacity=.75)
(vfield+surface).show(aspect_ratio=[1,1,1])
