Electrical Circuits

We are given a battery made of 12 cells, each with an emf of 5 V. Normally, when all the cells are connected correctly, the total emf of the battery would be the sum of the emfs of all the cells. In this case, the total emf with all cells connected in the same direction would be: Now, three cells are connected wrong, which means they are connected in the opposite direction. This will reduce the total emf, as the emfs of these cells will subtract from the total emf instead of adding to it. Each wrongly connected cell has an emf of 5 V, so the emf contributed by the three wrongly connected cells is: Since the wrong connection subtracts from the total emf, the resultant emf of the battery is: Thus, the resultant emf of the battery will be 30 V. Therefore, the correct answer is Option (B): 30 V.