A magnetic reed switch can only sense objects which generate a magnetic field.

• A. True
• B. False
• C. Sometimes
• D. Not at all

Answer: (A)

The main idea is that a magnetic reed switch closes only in the presence of a magnetic field. The reeds are actuated by magnetic flux, so a source must generate a magnetic field (such as a permanent magnet or a nearby electromagnet/current-carrying conductor) to make the switch operate. If there’s no magnetic field in the vicinity, the reeds stay open. Therefore, it’s accurate to say the switch can sense objects that generate a magnetic field, because without a magnetic field there’s nothing for the reeds to respond to. A non-magnetic object won’t trigger the switch on its own; the field must come from a magnetic source.