Which statement about electromechanical relays is true?

Which statement about electromechanical relays is true?

• A. They have no moving parts.
• B. They have moveable contacts.
• C. They are powered by gravity.
• D. They always fail open.

Answer: (B)

The action being tested is how an electromechanical relay operates. These devices use an electromagnetic coil to create a magnetic field that moves internal contacts, allowing a low-power control circuit to open or close a higher-power circuit. Because the motorized part of the relay is the movable contact and the armature that the magnet pulls, the key feature is that they have movable contacts. Springs or other mechanical parts return the contacts to their default position when the coil is de-energized, giving a defined off state. This is why the statement about movable contacts is true. The other descriptions don’t fit. They are not without moving parts—there are contacts and an armature that move. They aren’t powered by gravity; the actuation comes from the electromagnetic force in the coil, not from gravitational pull. And they don’t inherently fail in a single way; while a failure could be open, they can also fail closed (or weld shut) depending on wear, contamination, or overstress.

The action being tested is how an electromechanical relay operates. These devices use an electromagnetic coil to create a magnetic field that moves internal contacts, allowing a low-power control circuit to open or close a higher-power circuit. Because the motorized part of the relay is the movable contact and the armature that the magnet pulls, the key feature is that they have movable contacts. Springs or other mechanical parts return the contacts to their default position when the coil is de-energized, giving a defined off state. This is why the statement about movable contacts is true.

The other descriptions don’t fit. They are not without moving parts—there are contacts and an armature that move. They aren’t powered by gravity; the actuation comes from the electromagnetic force in the coil, not from gravitational pull. And they don’t inherently fail in a single way; while a failure could be open, they can also fail closed (or weld shut) depending on wear, contamination, or overstress.