Avery thin circular disk of radius r = 20.00 cm has charge q = 30.00 mc uniformly distributed on its surface. the disk rotates at a constant angular velocity ω = 5.00 rad/s around the z-axis through its center. calculate the magnitude of the magnetic field strength on the z axis at a distance d = 2.000 × 103 cm from the center. note that d > > r.