A coil of wire having finite inductance and resistance has a conducting ring placed coaxially within it. The coil is connected to a battery at time t=0, so that a time dependentcurrent I1(t) starts flowing through the coil. If l2(t) is the current induced in the ring and B(t) is the magnetic field at the axis of the coil due to l1(t), then as a function of time (t > 0), the product I2(t) B(t)