Ggiven a variable magnetic field b(r, t) = ηt4/s3ˆz [in cylindrical coordinates (s, φ, z)] where η is a constant, use ∇ × e = −∂b/∂t and ∇ · e = 0 directly to find e(r, t) in regions where the electron charge density rhoe = 0. assume that e is independent of z and φ with the boundary conditions es(s =