In memory logic circuits, which device is typically used to store a state?

• A. Lamp
• B. Control relay
• C. Push button
• D. Timer

Answer: (B)

Memory in logic circuits needs a device that can hold a state once a condition has occurred. A control relay provides that storage because its coil, once energized, can be held on by feedback through its own contacts, creating a latch. This allows the circuit to remember that it was activated even after the initial input is gone, until something resets it. A lamp is merely an indicator, not memory. A push button is an input device that sets or resets only while pressed, not a stored state by itself. A timer can create a temporary remembered state for a time, but it doesn’t serve as a general memory element storing a logic condition in the circuit. Therefore, the device typically used to store a state is the control relay.