Question

(a) How could you use a loudspeaker, a microphone, an oscilloscope and a signal generator to compare how well sound travel through different materials? Design an experiment to compare wood, glass and steel.

(b) State the precautions you would take to make sure your results were accurate.

(c) A singer wants to make one room in his house soundproof. This means that very little sound gets into or out of the room. How would the singer use the results of your experiment to decide which material to use?

Accepted Answer

(a) Experiment:

1. For this experiment we will need an oscilloscope, a signal generator, a loudspeaker, a microphone, connecting wires.
2. Connect the loudspeaker to the signal generator and the microphone to the oscilloscope as shown in the figure.

3. Adjust the signal generator to produce a sound of some frequency. Position the microphone and adjust the oscilloscope timebase and the volts per division setting so that several oscillations of the wave are visible.
4. Adjust x-shift and y-shift so that several oscillations are visible on screen. Calculate the time by multiplying the number of divisions by the timebase setting.
5. Calculate the time period for one wave oscillation by dividing the total time by the number of wave oscillations. Estimate the error in measurement.
6. Fix the ruler shown in figure and place the microphone on its stand.
7. Turn off the timebase. Connect the x-input of the oscilloscope to the output of the signal generator. It produces a series of patterns.
8. These patterns show the phase difference of the two signals. Adjust the microphone position along the ruler until the two waves on the screen are exactly in phase so they form a line positive gradient. Record the position of the microphone. Move the microphone exactly one wavelength along the ruler. When the two waves are in phase again you have moved through one wavelength. Measure the total distance moved and record the total number of wavelengths.

Result: Calculate the frequency of the wave by getting the reciprocal of time period. Calculate the wavelength by dividing the distance moved the number of wavelengths. The velocity of the sound wave is the product of frequency and wavelength.

There is air present as the medium of sound propagation between loudspeaker and microphone. We can place a wooden, glass or steel rod between the loudspeaker and microphone to get the speed of sound in these materials.

(b) Precautions:

1. All wiring should be checked.
2. Measurement error should be corrected.

(c) Glass is the best material for soundproofing because it is dense and non-porous, which means you get a lot of mass in a fairly small thickness. So, by calculating the speed of sound in different materials the singer will decide the best material that is glass for soundproofing the room.

Important Questions on Sound

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