A circular region in an xy plane is penetrated by a uniform magnetic field in the positive z direction. The field's magnitude B (in teslas) increases with time t (in seconds) according to B = at, where a is a constant. The magnitude E of the electric field set up by that increase in the magnetic field is given by the figure versus radial distance r; the vertical axis scale is set by Es = 350 UN/C, and the horizontal axis scale is set by Is = 8.50 cm. Find a. ES E (UN/C) 0 r (cm) ( =