Question

Many buildings and homes are equipped with magnetic locks. An electromagnet holds a metal door shut with the force of its attraction.



Some of these doors have a button placed nearby. Shortly after the button is pushed, the door is able to open. What does this button most likely do?
A.
It spins a permanent magnet near the electromagnet to cancel it out.
B.
It allows electricity to flow through the electromagnet for a certain amount of time.
C.
It stops the flow of electricity to the electromagnet for a certain amount of time.
D.
It releases an electromagnetic pulse, which momentarily disables the electromagnet.

Answer 1

C.

Electromagnets only hold when current flows. The push button most likely interrupts power (via a switch or relay) for a short time so the magnet loses its field and the door can be opened.