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Make a Simple Electric Buzzer

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An electric buzzer uses an electromagnet to make a loud repetitive sound.  Invented in 1831 by Joseph Henry, it is often used as a door bell or alarm.  Follow these steps to make your own buzzer.

Things You Need

Insulated wire
Wire stripper
Pair of scissors
Iron bolt
1.5-Volt C Battery
Electrical insulation tape
Metal can
Nail file
Cylindrical cork
Cardboard
Glue
Play clay
Pushpin
Rubber band
Paper clips
(Touch or hover over each item for more information or alternatives)

How To Make It

Buzzer 01 Buzzer 02 Buzzer 03 Buzzer 04 Buzzer 05 Buzzer 06 Buzzer 07 Buzzer 08 Buzzer 09 Buzzer 10 Buzzer 11

Things To Try

Connect your switch by turning the paper clip to touch the wire.  You should see the nail file start to move quickly back and forth between the bolt and the can.  Your buzzer produces sound when the nail file strikes the can.

Try changing the distance between the electromagnet and the nail file to find the best sound for your buzzer.

How It Works

When the switch is turned on, the battery's electric charge begins to flow through the coil around the bolt (an electromagnet), the nail file and the soda can (see Figure 1).  The bolt is immediately magnetized.  Since the nail file is magnetic, it is attracted towards the bolt.  When the nail file and the soda can are no longer touching, the electrical connection is broken and the electric charge stops flowing (see Figure 2).  This demagnetizes the bolt, causing the nail file to return back to its original position where it strikes the soda can to make a sound (see Figure 3).  The circuit is complete again and the the electric charges start to flow.  The cycle continues.  Each time the nail strikes back at the can, a sound is produced.  Depending on the distance between the electromagnet and the nail, the rigidity of the rubber band and the strength of the electromagnet, the circuit can be broken and completed several times a second.   Hence you hear a buzzing sound.

buzzer on
Figure 1: When the circuit is completed, the current flows from the battery, magnetizing the bolt (an electromagnet).
buzzer off
Figure 2: The electromagnet attracts the nail file, pulling it away from the soda can.  The circuit is broken when the nail file stops touching the can.
buzzer off
Figure 3: Without an electric charge flowing through the circuit, the electromagnet is no longer magnetic.  The nail file returns back to its position, striking the can to make a sound.  The circuit is complete again when the nail file touches the can. The cycle continues.

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Fun Facts

Loudspeakers

A loudspeaker converts electric signals into sound.  The sound that needs to be produced corresponds to an electric signal that is passed through an electromagnet.  Depending on the direction of the current, the electromagnet is either attracted towards or repelled away from a permanent magnet.  By switching the current direction at the correct frequency, the electromagnet and a thin membrane that is attached to it vibrate to produce sound waves.

Floating Trains

High speed maglev (magnetic levitation) trains use electromagnets for levitation (floating) and propulsion (moving forward) [3].  The train levitates when strong electromagnets on the tracks repel electromagnets underneath the train.  Another set of electromagnets along the track push and/or pull the train forward at incredible speeds using magnetic force.  The current record speed achived by a passenger maglev is 581 kilometers per hour (361 mph) set by JRMaglev of Japan [4].

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ReferenceReferences

[1] "Electrical buzzer." Wikipedia, The Free Encyclopedia. [Online]. Available: http://en.wikipedia.org/wiki/Electrical_buzzer. [Accessed: Jun 20, 2013].
[2] "Electromagnetism." Wikipedia, The Free Encyclopedia. [Online]. Available: http://en.wikipedia.org/wiki/Electromagnetism. [Accessed: Jun 20, 2013].
[3] "Maglev (transport)." Wikipedia, The Free Encyclopedia. [Online]. Available: http://en.wikipedia.org/wiki/Maglev_(transport). [Accessed: Jun 2, 2013].
[4] "JR-Maglev." Wikipedia, The Free Encyclopedia. [Online]. Available: http://en.wikipedia.org/wiki/JR-Maglev. [Accessed: Jun 2, 2013].
[5] N. Ardley, 101 great science experiments. DK Publishing, 2006