A parallel-plate capacitor with circular plates of radius R = 16 mm and gap width d = 5.0 mm has a uniform electric field between the plates. Starting at time t = 0, the potential difference between the two plates is V = (100 V)e-t/τ, where the time constant τ = 12 ms. At radial distance r = 0.80R from the central axis, what is the magnetic field magnitude?
(a) As a function of time for t ≥ 0
(b) At time t = 3t