Investigate and construct a sensor.

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AS LEVEL PHYSICS SENSING COURSEWORK

In this physics coursework, I have been asked to investigate and construct a sensor. I have chosen to examine sound and to develop and make a sensor, which would detect how loud specific rooms in the school, may be by the noise, which would be produced by a stereo system. I would create this sensor and compare my readings, which are produced, with the actual sensor used to detect how loud sound is. I would use this decibel meter and see how accurate my sensor is.

PLAN:

Aim: My aim of this experiment is to see how precise my sensor is compared to the real sensor that is the decibel meter. I would evaluate my sensor and compare the two sensors against each other using my results obtained.

Method: I had firstly planned to measure sound in different rooms in the school, by making the actual sound sensor. I had made this sensor by using a microphone, power pack, crocodile clips, ammeter and Voltmeter. I had connected this circuit up in series and then additionally added the microphone into the circuit. However when switching the power pack on, I found that there was a reading given by the voltmeter and not the ammeter. Therefore, I had thought about my experiment and realised that I needed to use a sound generator, loudspeaker and I needed to use the Oscilloscope. The previous attempt would not have worked as I recognized that I needed a loudspeaker, which would produce the different frequency of sound, and using the oscilloscope, I had connected the microphone up to this by crocodile clips and then placed the microphone near the loudspeaker so I could calibrate this sensor against the decibel meter. After doing this, I had taken my sensor to different rooms in the school and measured the sound by a stereo, which produced the sound.  This is a diagram of how my apparatus looked once set up to carry out my calibration:                          

 

         

This I thought was one way of carrying out this experiment, however there were other alternatives. I thought that I could also conduct this experiment by designing another circuit which would allow you to use a loudspeaker as a microphone. Sound waves reaching the speaker cone would cause fluctuations in a voice coil. This voice coil would move in the speaker’s magnetic field and would produce a small electrical signal. The circuit would be used with an operating voltage between 6 and 12 volts dc. This way would also give me a voltage reading and enable me to compare this against the decibel meter.  

        I had followed advice with my apparatus I had used, as I was not at first aware of how to use the signal generator, but my research had aided me to correctly use the signal generator. Additionally, I was also helped as I was not too sure how to set the oscilloscope up, however I overcame this and my experiment was set up correctly as shown in the diagram. I had experienced some problems when switching the oscilloscope on as I was alerted when I observed the frequency, which had not responded when I was speaking into the microphone, but I realised that I could change this setting and make the oscilloscope more responsive to the sound produced through the microphone.      

Experiment method: I had carried this experiment out by firstly connecting the oscilloscope to the microphone by using two crocodile clips, which connected the positive and negative through to the oscilloscope. After this, I had then connected the sound generator to the loudspeaker by again using two crocodile clips, which were plugged into the positive, and negative of the loudspeaker through to the input of the sound generator. I had then switched the oscilloscope on and had placed the microphone near the loud speaker. Following this I switched on the loudspeaker, set the sound frequency of the sound generator, and then heard a sound being produced. I would see the sound waves of the oscilloscope moves in an upright and downright direction, then measure how many bars the wave has consumed and then I would work out the voltage by diving the amount of bars by 0.5. In addition, I would be recording this in a table, and this would show the voltage against decibels. I would also measure this with the decibel meter by simply placing this the same distance as the microphone away from the loudspeaker. I would be increasing the sound frequency and working out the voltage and measure this using the decibel meter. This process has to be done so that my sensor is calibrated with the decibel meter that is why I am recording the decibels against voltage so I can plot a calibration curve.

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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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