$21.$A square coil with $10$ cm of side has $30$ turns of wire. Initially it is at rest between two poles of a magnet where the field is $0\mathrm{.}60$ T $,$ with the plane of the coil perpendicular to the field. What average voltage is produced on the coil if it is withdrawn completely from the field? What was the voltage before removing the coil when it was at rest? If the resistance of the wire is $20,$ what is the current of the coil?