The figure shows an LR circuit with a switch and a 240-volt battery. At the instant the switch is closed the current in the circuit and the potential difference between points a and b, Vab, are
a. 0 A, 0 V b. 0 A, -240 V c. 0 A, +240 V d. 0.024 A, 0 V e. 0.024 A, +240 V
Answer : c. 0 A, +240 V
When the battery discharging, the voltage will drop continuously, the voltage across a and b at the start instant should be equal to the original voltage of the battery 240V. However, how can we determine whether Vab is +240V or -240V?
Moreover, if the potential different at the start instant is 240V, why should the current equals 0A?
Thank you for your help.