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I have decided to choose and investigate; "exploring the characteristics of a sensor."

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Instrumentation Task

Characteristics of an LDR


This Instrumentation task is an independent project, aiming to demonstrate my practical, experimental and planning skills. I have the choice of three options in which to do so, and they are as follows…

  • Building and testing a sensor
  • Exploring the characteristics of a sensor
  • Designing and assembling a measurement system, and using the sensor to make a measurement

From these alternatives I have decided to choose and investigate; “exploring the characteristics of a sensor.” I have chosen this criteria as I think I can relate my physics thoughts and experimental skills to this I can relate my physics thoughts and experimental skills to this aspect well. I will decide on a simple sensor so I can use its properties to perform an affective instrumentation task.

I contemplated on doing the other two tasks, as I feel they are a little impractical and I cannot perform them scientifically as well as the characteristics of a sensor.

How will I perform this task?

From the sensors that are available to me I have decided to choose an LDR (Light Dependent Resistor). This is a light detecting sensor in which can be set up simply in a circuit, to explore a characteristic of its properties.

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Once the apparatus are set up and all fair test procedures are complete, I must obtain the results. I decided to start the LDR 40 cm away from the light source, and work down to 40 cm. This is so I can just simply cut down the black out tube, rather than re-make it. I will work down from 40cm – 10cm in 2 cm’s at a time. Any less would be a little impractical and irrelevant, but any more could affect the general pattern to the results. I will simply tape the LDR to the ruler as I move it down, and record the readings in a suitable table. The ruler and ray box will be taped down at all times, throught out the experiment.

The readings in which I will record are the voltage across the LDR and the current in the LDR circuit. By doing s o I can calculate the resistance using the formula: Ω = V/I, after the experiment.


Generally, I predict that as the light intensity increases the resistance will decrease, resolving the current to decrease as well. I know this due to previous education in physics lessons. Basically as the LDR gets closer to the light source the light intensity increases.

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To resolve this problem I decided to lower the Voltage to the LDR and so I could use a milli-meter for most of the experiment. This way when dividing the voltage by the current to get the resistance, the gaps between the results will not be as high. This is what Results 3 show, and as you can see by the graph it produces a clear equal increase of resistance in the LDR.


Overall I believe my experiment to be a success, the results were fairly accurate as they followed my prediction and conclusion. However, there was one anomalous result with in the second set of results. At 22cm away from the light source the current increased to 0.04 from 0.03, when in theory it such have decreased. But this little anomaly didn’t prove to be a problem and did not affect the experiment as a whole.

If I was to perform this experiment again I think I would perhaps investigate one other characteristic of an LDR and compare my results. Maybe I could use the LDR and a resistor to form a potential divider to make a light sensor, and see how the brightness of light affects the resistance. This way I could view two different experiments and see which will affect the resistance greater.


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