Which statement best describes a magnetic reed switch?

• A. They are mechanical devices with moving parts.
• B. They are electronic devices with no moving parts.
• C. They rely on light to detect magnetic fields.
• D. They are acoustic sensors.

Answer: (A)

Magnetic reed switches are magnetic field-activated switches that use two thin metal reeds sealed in a glass envelope. When a magnet is nearby, the reeds attract and touch, closing the contacts and completing the circuit; when the magnet is removed, they separate and the circuit opens. This reliance on the physical movement of internal contacts makes them mechanical devices with moving parts. They aren’t electronic switches with no moving parts, they don’t detect magnetic fields by light, and they aren’t acoustic sensors.