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 releases an electromagnetic pulse, which momentarily disables the electromagnet.
B.
It spins a permanent magnet near the electromagnet to cancel it out.
C.
It stops the flow of electricity to the electromagnet for a certain amount of time.
D.
It allows electricity to flow through the electromagnet for a certain amount of time.

Answer 1

C.

An electromagnet only holds the door shut while current flows through it. Pushing the button most likely interrupts the current (often via a relay or controller) for a short time, removing the magnetic field so the door can be opened.