Electromagnetic release in alarm system

Steps:

• Switch S closed energizes electromagnet, attracting and holding soft iron contact upward, preventing bell circuit completion.
• Opening switch S de-energizes electromagnet, releasing soft iron contact.
• Released contact drops due to gravity, completing bell circuit.
• Current flows through bell, causing it to ring continuously.

Why A is correct:

• In alarm systems, de-energizing the holding electromagnet allows the contact to drop and close the circuit, activating the bell per electromagnetic induction principles.

Why the others are wrong:

• B: "Drops up" is physically impossible; bell stops incorrectly as circuit activates.
• C: Contact moves down (drops), not up; bell rings, not stops.
• D: Contact drops, not moves up; bell rings, not stops.

Final answer: A