Magnets: The Heart of a Successful Ding Dong Ditch

Your heart is beating rapidly, a dribble of sweat slowly slides down your face as you run up the porch to the door. You hit the doorbell, "ding dong!", a light turns on in the house and the owner gets up to go to the door, you bolt. You're panting and your legs are burning by the time you round the corner and meet up with your friends. You receive a round of high fives and one friend yells, "Nice job ding dong ditching the old lady!" This ding dong ditch would not be possible without magnets!

Doorbells use magnets to create a ring or buzz sound when a visitor is at your front door. When the button is pushed it completes the circuit inside the wall so the flow of electricity goes through the electromagnets to a transformer then to the electromagnet wires. From here the magnetism of the wires attracts an iron bar that is connected to a "contact arm". This contact arm is lifted off of it's metal resting place, or contact (a small piece of metal located just under the contact arm), causing the circuit to break and the contact arm to fall. When the contact arm hits the contact the circuit is then reconnected and the entire process starts over again.

A sound is heard because the contact arm is moving back and forth so quickly between the contact and the bar around the electromagnet, that a buzzing sound is heard when it hits either objects. The process is very similar when a bell is heard rather than a buzz. The only difference is that the contact arm hits a clapper which hits a bell instead of the contact arm just hitting the electromagnet (see diagram above). Similarly once the contact arm falls and hits the contact thecircuit is restored and the process repeats.

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Diagram of the inside of a doorbell that makes a bell sound.The sound is created by the clapper hitting the bell.

When a chime or a "ding dong" is heard the set up is a little different. In a chime doorbell there is a solenoid, a wire coil wrapped around a magnetic metal, instead of an electromagnet. In the middle of this solenoid there is an iron piston. At the end of this iron piston is a spring coil and on either side of the piston there are two bars (the piston and two bars at the ends are separated by a small amount of space), which when hit creates noise. When the button is pressed the solenoid is filled with a current and becomes magnetized. This makes the iron piston become a magnet and it is drawn to one of the bars (it is drawn to the bar farthest from the spring on the piston). When the piston and bar collide it creates a chime. The piston will stayed magnetized to the bar until the button is released. When the button is released the spring pulls the piston back until it hits the bar on the opposite side causing the second chime to be heard. So the next time you visit a friend and feverishly ring the doorbell think of the physics behind it. (If you are still confused about how a doorbell works check out the video above for further clarification. It describes how a doorbell works through a more visual interpretation.)




Works Cited:Google Image Result for Http:static.howstuffworks.com/gif/doorbell-bell.gif." Google. Web. 20 Mar. 2011. <http://www.google.com/imgres?imgurl=http:static.howstuffworks.com/gif/doorbell-bell.gif&imgrefurl=http://home.howstuffworks.com/home-improvement/repair/doorbell2.htm&usg=__59X8h0xNXKvwWkYieKcTWqFtxJ8=&h=396&w=398&sz=37&hl=en&start=0&zoom=1&tbnid=DhONRB_do-I-aM:&tbnh=134&tbnw=135&ei=6ZiGTduoMtPegQe-sNHECA&prev=/images?q=inside+a+doorbell&hl=en&biw=1440&bih=733&gbv=2&tbs=isch:1&itbs=1&iact=rc&dur=506&oei=6ZiGTduoMtPegQe-sNHECA&page=1&ndsp=30&ved=1t:429,r:3,s:0&tx=64&ty=59>."HowStuffWorks "How Doorbells Work"" Howstuffworks "Home and Garden" Web. 18 Mar. 2011. <http://home.howstuffworks.com/home-improvement/repair/doorbell3.htm>.
"YouTube - Electromagnetism Pt 1 (how a Doorbell Works)." YouTube - Broadcast Yourself.Web. 20 Mar. 2011. <http://www.youtube.com/watch?v=0yDxZD0RlLI>.