Which statement best contrasts relays vs solid-state outputs?

• A. Relays have mechanical contacts; Solid state use electronic switches.
• B. Relays require continuous power.
• C. Solid state outputs always require external cooling.
• D. Both types are identical in operation.

Answer: (A)

Relays switch via mechanical contacts that physically open and close when the coil is energized, while solid-state outputs use electronic semiconductors to switch with no moving parts. This fundamental difference is why the statement is the best: relays rely on physical contact, which can wear out and arc, whereas solid-state devices switch electronically, offering fast, wear-free operation (but with potential leakage currents and heat that must be managed). The other points don’t capture this essential contrast, since power needs, cooling, and identical operation are not defining features of how the two switching methods differ.