Which of the following devices is used to measure linear displacements?

The Linear Variable Differential Transformer (LVDT) is a highly effective device for measuring linear displacements. It operates on the principle of electromagnetic induction and provides a highly accurate measurement of an object's position along a straight line. In its basic form, the LVDT consists of a primary coil and two secondary coils positioned symmetrically around it. When an object moved by the displacement enters the LVDT's core, it alters the magnetic flux linking the coils, resulting in a differential output voltage that is proportional to the displacement of the core.

This method allows for the measurement of precise linear movements without any physical contact, making LVDTs well-suited for applications where precision is critical, such as in industrial equipment, automotive systems, and aerospace applications. Furthermore, the LVDT's robust construction and ability to function in harsh environments add to its practicality for various engineering uses.

In contrast, a pressure gauge measures pressure rather than displacement, a thermometer measures temperature, and a flow meter gauges the flow rate of liquids or gases. Each of these devices serves specific purposes that do not align with measuring linear displacements. Therefore, the LVDT is the correct choice for accurately measuring linear displacements in power engineering and related fields.