There's a problem in Electricity I cant seem to figure out: A charged ring of radius 40 cm has a gap of 4 cm. Determine the electric field, at the center of the ring, when it carries a charge of 2 coulombs. I think that the linear charge density doesnt change much because of the small size of the gap ( compared to the radius of the ring) . Linear Charge Density = Lambda = Q / L , L = 2(Pi)(R) - 0.04 = 2(Pi)R The problem is, however, that I cant seem to figure out how to determine the electric field inside a ring. We have only worked with spheres, where we chose a Gaussian surface of a sphere ( of r > or < than R ) and then calculated E. In the case of a ring, what type of gaussian surface should I choose?