The α value for a ZnO varistor is 15 and kI = 9:3 10-38, the potential difference and current being measured in volts and amps respectively. Calculate the p.d. across the varistor for currents of 0.1, 1, 10, 100 and 1000 A. If a device needs protection against transient voltages in excess of 300 V, show how a varistor having the characteristic defined above can be connected to afford protection.