Which component is an electromagnetic coil with a movable plunger?

• A. Tachometer
• B. Solenoid
• C. Tertiary Winding
• D. Transformer

Answer: (B)

A solenoid is an electromagnetic coil designed to produce linear motion with a movable plunger. When current flows through the coil, it creates a magnetic field that pulls the plunger in or pushes it out, converting electrical energy into mechanical displacement. This makes it an actuator, used to operate valves, switches, or interlocks in rail systems and other equipment.

In contrast, a tachometer measures rotational speed, not actuating motion. A transformer transfers electrical energy between circuits using fixed windings and a core, with no moving parts. A tertiary winding is simply an auxiliary winding within a transformer used for additional voltage, again without any moving component. Therefore, the device described as an electromagnetic coil with a movable plunger is a solenoid.