ANS:C - mutual inductance

The working principle of a Linear Variable Differential Transformer (LVDT) is based on the principle of mutual inductance. An LVDT consists of a primary coil, two secondary coils, and a movable core. When an alternating current (AC) is passed through the primary coil, it induces voltages in the two secondary coils, which are connected in series opposition. The voltages induced in the secondary coils vary with the position of the movable core. As the core moves, it changes the coupling between the primary and secondary coils, altering the mutual inductance between them. By measuring the difference in voltage between the two secondary coils, the displacement or position of the core can be determined. LVDTs are widely used as displacement sensors in various applications due to their accuracy, reliability, and robustness. Therefore, the correct choice is: mutual inductance