Question

In the circuit shown potential difference between x and y will be:

A.) zero
B.) 20 V
C.) 60 V
D.) 120 V

Answer 1

Hint : The concept of open circuit can be used in this case. An open circuit implies that the two terminals or points are externally disconnected, which is equivalent to a resistance $ R=\infty $ . This means that zero current can flow between the two terminals, regardless of any voltage difference.

Complete step by step answer

We know that the magnitude of emf is equal to V (potential difference) across the cell terminals when no current is flowing through the circuit i.e. when the
As the circuit is open at points A and B, no current is flowing through both the resistances and therefore, the potential drop across both of them is zero.
Thus, potential difference between these two points is equal to the potential across the cell terminals i.e. 120V.
Thus, option D is correct.

Note
If say, any number of resistances are given in this circuit, even then the answer would be the same i.e. equal to the potential across the terminals of the battery. We do not need to consider the values of the resistances given and answers can be given directly.
Imagine a situation in which we join both the terminals X and Y (as shown in figure) and then try to calculate the potential difference between these two points so the answer would be zero. Because in this situation a short circuit between X and Y has occurred.