Plane figures made of thin wires of resistance $R = 50\,\,milli\,{\rm{ }}ohm/metre$ are located in a uniform magnetic field perpendicular into the plane of the figures and which decrease at the rate $dB/dt = 0.1\,\,m{\rm{ }}T/s$. The current in the inner and outer boundary are inner radius $a = 10\,\,cm$ and outer radius $b = 20\,\,cm$)<br />.