Once doing this, I would then take my oscilloscope connected to the microphone around to the different rooms in the school, and measure the sound produced by a stereo in the given room and measure the sound by using the microphone which would detect the sound and would enter the oscilloscope allowing me to produce the voltage reading. I would also take the decibel meter and measure the sound in the room, so I can have two results for each room, which would allow me to compare the sensors.
Apparatus used: I had used the following equipment:
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Decibel meter
- Stereo
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Crocodile clips
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Oscilloscope
- A sound generator
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A loudspeaker
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A microphone
How I will make this experiment safe: I will ensure that I keep this experiment safe by making sure that the music which is played in the five different rooms are not exceedingly high, as this can be dangerous if too high so I will keep the volume at the same moderate level. I will also place the oscilloscope on a table and not hold this as this may result in falling and breaking. To reduce danger I will make sure that I have connected the crocodile clips securely to the oscilloscope and that the plug is earthed so the fuse cannot blow. Before switching the oscilloscope on, I will check the connections are secure.
I would make sure I reduce uncertainties (errors) by making sure that this experiment is conducted in a fair test, and I would do this by making sure I use the same equipments every time, and I would keep the stereo volume the same in every room. I would also make sure I carry this experiment out accurately by making sure that I place the microphone 5cm away from the stereo and the decibel meter 5cm away from the stereo, this will enable me to get an accurate results for all of the rooms from which I have chosen.
PHYSICS
We can see much physics involved in the crystal microphone, which I will be using as this component itself is a sound sensor. This is how the crystal microphone works and processes sound when it detects it:
The crystal microphone uses piezoelectric crystals, in which a voltage develops between two faces of the crystal when pressure is applied to the crystal. In this, microphone sound waves vibrate a diaphragm, which in turn varies the pressure on a piezoelectric crystal. This generates a small voltage, which is then amplified. Here is a diagram to show the crystal microphone, which will be used:
The piezoelectric crystal is what is used in ultrasound, this vibrates very fast and produces the high vibrations, if just the crystal is placed into a circuit containing a voltmeter as shown we can see that this element alone has very distinctive properties as it can generate electricity by a slight force applied.
A microphone wants to take varying pressure waves in the air and convert them into varying electrical signals. The crystal microphone is commonly used to accomplish this conversion:
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Crystal microphone - Certain crystals change their electrical properties as they change shape. By attaching a diaphragm to a crystal, the crystal will create a signal when sound waves hit the diaphragm.
As you can see, just about every technology imaginable has been attached to convert sound waves into electrical signals. The one thing they all have in common is the diaphragm, which collects the sound waves and creates movement in whatever technology is being used to create the signal.
Sound travels through the air by making air molecules vibrate and bump into one another. We hear a sound when the vibration has been passed along all the air molecules from the source of the sound to the molecules near our ear. When the air molecules near our eardrum vibrate they bang against it, making it vibrate, and our nerves detect this vibration, carrying a message to our brain. A microphone works in much the same way. It consists of a very thin sheet of plastic, called the diaphragm, which vibrates when air molecules hit it. The diaphragm is positively charged. Behind the diaphragm is a metal back plate that is negatively charged, attached to a circuit. As the diaphragm moves, it induces more or less charge on the metal plate behind it, producing an alternating signal in the electric circuit. In this experiment, I would also be connecting the microphone up to the oscilloscope and this would detect voltage given by the microphone in the simple circuit. An electron beam is swept across a screen horizontally (X direction) at a known rate (perhaps one sweep per millisecond). An input signal is used to change the position of the beam in the Y direction. The trace left behind can be used to measure the voltage of the input signal (off the Y axis) and the duration or frequency can be read off the X-axis. Therefore, this would show the waves of sound in a simple diagram and from this I would be able to calculate the voltage of the sound given off in the five different rooms in the school I have chosen. Here is a diagram showing what the sound waves, which would be produced, would roughly look like on the oscilloscope:
I have used my equipment with skill as I had firstly tested my oscilloscope along with the decibel meter to check it was working so that my results would not be in danger of being incorrect. I individually checked all of my apparatus to see that it had function properly. I had done this by using my crocodile clips and connecting this to the microphone, and then I connected this to the oscilloscope. I spoke into the microphone and checked that this had recorded as sound waves into the oscilloscope. Additionally, I had checked the accuracy of my decibel meter as I had made a series of sounds I checked the decibels were reading high and low. I had applied these same methods to my microphone.
I would carry out a range of experiments as when measuring the sounds in different rooms in the school with the microphone attached to the oscilloscope and the decibel meter I would take three reading for the voltage and three readings for the decibel meter. Therefore, from this I would have three readings showing the voltage and decibels in each room in the school. From this I would be able to calculate accurate results from an average. I had realised I may overcome some problems while conducting the experiments like the temperature variation in the room and the dust. To overcome the problems I had made sure carried out this experiment in the same room and that the temperature was at the standard room temperature. The temperature could affect my results in the slight way as this would not be a fair test and the humidity can alter the wavelength of the sound, as the molecule vibrations would be effected by the heat. Also the dust, which can affect the wavelength and frequency. These would both affect my results.
OBSERVATIONS:
I had obtained results from the calibration, this is where I had calibrated my made sensor against the decibel meter. I had recorded the voltage of my sensor through the oscilloscope against the decibels given from the decibel meter through different sound frequencies.
I also obtained results from my preliminary, which I carried out this experiment as a practice test, to see whether everything had gone accordingly to plan. Additionally I carried out my experiment where I had taken the experiment out three times and then calculated my average from this, which had given me accurate results. Here are the table showing my results from the calibration, preliminary and the actual experiment: (My results are taken to three decimal places)
Calibration results table:
Preliminary results table:
Actual experiment results:
My graph shows how I had started the experiment off, as I had calibrated my sensor with my decibel meter. I had then processed with the preliminary task where I had gone to the various five rooms in the school and had placed the stereo I the centre of the room and recorded the voltage using my sensor which contained the oscilloscope and the microphone, and using the decibel meter I had recorded the amount decibels. I had taken these two readings so that I could compare my readings in voltage and convert them into decibels and then simply compare the two sensors and see how accurate my sensor I constructed was against the decibel meter.
Graph: From the calibration table I have produced a graph, which shows the voltage against the decibels. You can see that it is illustrated simply as the voltage increases so does the decibels, therefore they are proportional, as if one increases so would the other. I had drawn a curve, which goes through the points, which I had obtained from my calibration results. This is so that I could compare my readings as I would convert my voltage into decibels and see how accurate they were to the real decibel readings on the table. From this graph, we can identify that sound in decibels seems to increase at first, but as the voltage increases we can see that the decibels increase but by a small amount so there is not such a great peak in the graph.
Comparing my sound sensor against the decibel meter: From these above results I can now compare the two sensors and distinguish how accurate my sound sensor actually is. However, in order to achieve this I will need to convert my results from the voltage to decibels, and this is where I would use my calibration graph to find this out. Using the graph, I would look at the voltage I had achieved in the different rooms in the school, and on the X-axis, I would go up the voltage until it meets the curve I had drawn, I would go across and see where this meets the decibel on the Y-axis. This reading would be the conversion from voltage to decibels and I would compare these reading to the decibel obtained form the actual decibel meter. Here is a table showing the average voltage and decibels obtained in the different rooms in the school as shown above, but here I have added the conversion from voltage into decibels:
From this table I can work out the Percentage error between my sensor conversion in decibels and the actual decibels taken from the decibel meter. To find the percentage error from this I would simply find the difference between the decibels and then divide the difference over the reading taken from the actual decibel meter, and then multiply this by 100.This is shown in the table:
Here I have calculated the percentage error for each of the results, to find how inaccurate or accurate my sensor is to the decibel meter. I will calculate the overall percentage error by adding up my percentage differences all together and then dividing them by the number of answers I have, which is five.
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9.9+19.7+2.1+9.9+3.0= 44.6 / 5= 8.9% overall percentage error difference between my sensor and the decibel meter.
From this we can see that my sensor I had constructed is 8.9% less accurate the decibel meter, so my sensor is quite accurate compared to the real sensor. I had dealt with uncertainties such as humidity as I made sure I kept the room at a set temperature so there would be no molecular change in the molecules as if the temperature had varied then my results would be unstable when going to the different rooms in the school. When there is a change is molecular configuration then sound would be affected as the sound waves, which enter the microphone would be diverse. So, I made sure that all rooms I done this experiment in was at a constant temperature. Dust was another uncertainty, but I made sure that all the rooms were clean of dust as again this could disturb the sound waves and molecules in the air. So I made sure that this experiment was fair in the sense that I made sure all rooms were at a constant temperature free of dust and also that there was no other sound interference apart from the stereo which had played the same music. I had controlled the sound interference as I had carried out this experiment after school when everyone had gone, so there were no interferences, as if there was then my results would not be entirely accurate as extra sound would give false results, making my experiment unfair. Therefore, I had made sure that I dealt with these uncertainties.
ANALYSIS
When I had carried out this experiment, I had taken extreme care over my apparatus set-up, as I had made sure that I had made this as accurate as I could possibly make it. I had ensured this because I had wanted my results to be extremely accurate as I could make them, since this is what would help me discover how accurate my sensor is compared to the decibel meter. To achieve accurate results I had recorded my results three times, in each room in the school so I could then figure out an average, which I had used to calculate the percentage error of my sensor. Through taking a series of results, I felt that this would help me to gather results, which were averaged out because if I had just taken one set of results I would of experienced some errors in these results. Moreover, they would not be found and would simply give false indications of whether my sensor was good and accurate or was not very accurate.
Through my results, I had achieved an anomaly, which appears up in the calibration graph, as this is shown up where it looks as though this reading may have been slightly inaccurate due to the change of equipment on a different day when conducting this. This reading does not really flow through my hand drawn curve and I believe that this result had consequently ended up not fitting in the trend as it may have been due to human error in the results, or maybe even the conductivity of the leads I had used, as the resistance may have lead to systematic error. There is not much I could have done to prevent this, but I feel that my results obtained from my sensor indicate that it is a successful and accurate sensor compared to the decibel meter. I believe that in this experiment my results seemed fairly accurate and I had ensured that this experiment was taken under the right conditions as I made sure that it was a fair test and this is what I believe led to the accurate results I had achieved.
I believe that the sensor I have constructed is successful; as I found that, it was accurate compared to the decibel meter, which was perfect. The sensor, which I made
had a high resolution as it had detected very small changes, however the resolution seemed to be lower compared to the decibel meter as this sensor would have a very high resolution as it detects sound changes far more easily and accurately by the great components which are used. This indicates that when music is played my designed sensor would be able to detect the change in the quietness and the sound waves produced by the music, which is played and detected. In addition, my sensor I had designed is quite sensitive but it is not needed to make it less sensitive when it detects the sound, the sensor I had designed is sensitive enough to detect sound from a average distance. This quality I believe is what makes it a good sensor system as it is sensitive enough to detect the sound without no alterations needed, and also it has a high resolution and is accurate enough to give a sensible realistic reading. The response time in my sensor was very short, so that if I had changed the sound instantly this would appear up on the voltmeter, as the crystal microphone is a very good sensor of sound and this would instantly be shown up on the voltmeter when there is a rapid change. The data from this sensor system must be processed, often with appropriate averaging and however this does not have to be displayed to show an effective picture.
I believe that I could have improved this experiment by carrying out more research to how I could have improved my sensor by making it more accurate. In addition, I also deem that I could have also used better equipment, as this would have improved my results, as they would be more accurate as when I used the crocodile clips I noticed the resistance would have varied and this would have affected my results. Overall, I believe that my sensor was accurate compared to the decibel meter, as I found that in the given time I was allowed I had built a sound sensor which proved to being accurate and easy to use jus like the decibel meter.
BIBLIOGRAPHY
I had achieved information required for this coursework from the following:
- Advancing Physics AS
- Britannica Encyclopaedia
- Encarta encyclopaedia on the internet
I found that the information from these sources seemed very reliable and information I had gained, helped me understand the complex issues with the relation of physics to sensing. I had obtained the various information I have included on the background information on the sensor from the following Internet sites: