A very long Teflon rod (cylindrical in shape) is held in water. The radius of the rod is 20 mm. An external electrostatic field exists in the water and is E = 3x + 5y (volts/meter). If the rod is aligned with the z-axis, come up with an expression for the surface charge density on the surface of the rod. [εTeflon = 2.1εo and εwater = 81εo]