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Speed of Sound Measurement Through a Simple Experiment

written by: Swagatam • edited by: Lamar Stonecypher • updated: 2/22/2010

In school and college we all must have studied a lot regarding “sound" and its properties. We have also learnt how sound propagates and its traveling speed in the air. In this article we will discuss about an experiment to measure the speed of sound.

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    What is Sound?

    In simple words, any physical vibration produced in the air will constitute a sound. A sound, for example made by clapping of hands, creates sudden compressions in the air, these are converted into vibration patterns which moves through the air, reaches our ear drums and are translated as sound waves into our brain. Experiments have proved that typically sound waves travel at a speed of 340 meters per second. An experiment to measure the speed of sound can prove the above fact. It can be very easily conducted through a simple electronic circuit set up.

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    How to Set Up the Electronic Circuit for the Experiment


    The circuit basically can be divided into two sections, viz. a sound sensor or the receiver and an electronic stop watch timer. Let’s see how the required adjustments are made in the circuit through the following steps:

    • To begin with, complete the assembly of a simple electronic circuit as per the circuit schematic.

    • You will just have to solder all the shown components over a general purpose board according to the diagram. Make sure that all the connections are done correctly.

    • After completing the board assembly, initially keep the link between the sound sensor section and stop watch timer section open, so that they can be tested separately.

    • Connect a 12 volt battery to the supply terminals of the circuit. Immediately you will find that each LED is getting illuminated and shifting sequentially from first to the last (27th) LED at a certain unidentified rate.

    • Adjust the value of the potentiometer to get a clock pulse of exactly 27 Hz at the clock input of the IC 4017. The procedure is best done by connecting a frequency meter at the clock input.

    • This will make the 27th LED or may be the 26th LED to light up sequentially after a span of exactly one second.

    • Also, dividing a second by the order number of the LED that is lit, will give the rate at which the LEDs are shifting.

    • Next, check the sound sensor section by giving a gentle tap over the mic. The LED connected at its output should instantly light up and remain latched.

    • Disconnect the power from the circuit and join the link between the two sections. These are the only required adjustments in the circuit part.

    To make sure that the experiment to measure the speed of sound gives the right results, the above adjustments should be concluded very accurately.

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    How to measure the speed of sound?

    For the experiment, along with the above circuit set up you will require a powerful car horn, 12 Volt automobile battery, around 100 meters of wire and a push-to-ON switch. Also, you will need to find a suitable secluded place, free from any noise pollution, so that the experiment can be carried out without any spurious results. The experiment is completed in the following manner:

    • Lay down the 100 meters wire, so that it covers the full 100 meters of ground length.

    • Connect the ON/OFF switch, the horn and the battery to one end of the wire as per the diagram.

    • Connect the electronic circuit assembly to the other end of the 100 meters wire. Align the circuit such that the mic is exactly in line with the horn 100 meters away.

    • The set up for the experiment is now ready. The final step may now be executed.

    • Press and release the push-to-ON switch to activate the horn for a second.

    • The circuit will immediately respond to the horn and a particular LED out of the 27 LEDs will be lit and latched.

    • By dividing 1 (second) by the order number of the LED which is lit, the time taken by the sound from the car horn to travel a distance of 100 meters can be easily calculated.

    • By multiplying the result with 10 the speed of sound per second may be also be known.

    The above experiment to measure the speed of sound is the most simple and accurate way of calculating the speed of sound.