Question

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

Explanation:

Typically, these doors are held closed by an electromagnet. Pushing the button must disable the electromagnet to allow the door to open. Stopping the flow of electricity to the electromagnet for a short - time would disable it, enabling the door to open. Options B, C, and D are less common and more complex ways to achieve the same result.

Answer:

A. It stops the flow of electricity to the electromagnet for a certain amount of time.