A storage battery is marked "1200 Wh, 12 V".
Answer the following questions with suitable reasoning.
a. (i) Explain the physical meaning of the figures 1200 Wh and 12 V written on the battery.
b. (ii) Starting from the definition of electrical power and electrical energy, show that the time for which a device of constant power P can be run by this battery is given by t=P1200Wh, provided the battery is ideal.
c. (iii) The battery actually delivers energy with an overall efficiency of only 85 %. Explain qualitatively how this efficiency alters the running time obtained in part (ii).