Depth Study – Electromagnetism in Doorbells (R.C)

Resource Description

Operation of the doorbell in terms of electromagnetism (Operation of a doorbell in electric and magnetic interactions)

Electromagnetism is the interaction of electric currents (electrons moving through a conductor) with magnetic fields (1). It is also the basis of how a doorbell works, as is shown in the model made. A doorbell is an open circuit, and it closes when the doorbell button is pushed (as shown in the model). Electricity then flows from the house circuit and through the ‘step down’ transformer (2) which lowers the voltage to a more usable amount (typically 10 to 20 volts in a doorbell) (3, 4). The current then flows through the electromagnet, causing it to magnetise. This attracts the iron section of the arm (represented by a metal straw on the model) towards the electromagnet, but it is stopped by the clapper hitting the gong, which makes the doorbell sound (the arm in the model represents this – it can move!) (4, 5, 6). The movement of the arm disrupts the electrical contact between arm and a stationary part of the circuit, stopping the current flow and the electromagnet (4, 7, 8). Without the magnetic pull of the electromagnets pull, the arm falls back to its original position due to the the stiffness of the spring (9). Since the circuit is once again closed, the current flows and the process starts again. This process happens very quickly, 10 – 20 times per second, which causes the buzzing sound in a buzzer doorbell (4, 5, 7) Electromagnetism is the study of how electricity and magnetism are related, and is an extremely important factor in the operation of a doorbell, and can be explained using Faraday’s Law. Faraday’s Law says when the north end of a magnet approaches a coil of wire, the induced current (current in the wire caused by the magnet) flows to oppose this force. The section of wire closest to the magnet becomes positively charged, so the electrons flow in the opposite direction (causing a current) (17, 18, 12).