Question

A circular region in an xy plane is penetrated by a uniform magnetic field in the positive direction of the z axis. 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 Fig. 30-55 versus radial distance r ; the vertical axis scale is set by Es = 300 µN/C, and the horizontal axis scale is set by rs = 4.00 cm. Find a.