In the persistent current experiment described in Section 10.5, let us assume that the current persisted without detectable reduction for exactly 2.5 years. Given that the inductance of the ring was approxi-mately 3.14 X 10-8 H and the sensitivity of the current measurement was 1 part in 109,
(a) estimate an upper bound for the resistance of the ring and
(b) estimate how long at least 90% of the current would be certain to remain.