In the circuit shown if figure, `XY` is potentiometer wire `100 cm` long. The circuit is connected as shown. With switches `S_(2)` and `S_(3)` open, a balance point is found at `Z`. After switched `S_(1)` has remained closed for some time, it is found that contact at `Z` must be moved towards `Y` to maintain a balance. which of the following in most likely reason for this ?

Options

A. The cell `V_(1)` is running down
B. The cell `V_(2)` is running down
C. The wire `XZ` is getting warm and its resistance is increasing
D. The resistor `R_(1)` is getting warm and increasing in value.

Answer

A

Explanation

(a) If `V_(1)` decrease, then potential differential across `xz` will decrease. So to have same potential difference i.e., `V_(2)` across `xz`, length `xz` has to be increased or `z` should be moved towares `y`.
(b) is correct, because for this `z` should have been moved toward `x`.
(c ) Will be incorrect because `xz` can get warm up if current through it increase which is not possible.
(d) is incorrect, because which is no current in `R_(1)`.