Which of the following statements is FALSE? A. In a balanced...

In a balanced Wheatstone bridge, the condition for zero deflection in the galvanometer is $\dfrac{P}{Q} = \dfrac{R}{S}$.

If the cell and the galvanometer are exchanged, the new condition for balance becomes $\dfrac{P}{R} = \dfrac{Q}{S}$, which is mathematically identical to the original condition. Therefore, the bridge remains balanced and the null point is not disturbed.

Statement A is false.

A rheostat can be used as a potential divider by connecting the source across its fixed terminals and taking the output across one fixed terminal and the variable terminal. Statement B is true.

Kirchhoff's second law (loop rule) is based on the law of conservation of energy. Statement C is true.

A Wheatstone bridge is most sensitive when all four resistances are of the same order of magnitude. Statement D is true.

Answer: A