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# A light Dependent Resistor Essay

Custom Student Mr. Teacher ENG 1001-04 13 October 2017

## A light Dependent Resistor

The end of the bulb was always 10cm from the LDR. Method: 1. Set up apparatus as shown: The bulb should be aligned so that it is clamped 0. 1m directly above the LDR- this is difficult to represent on the diagram. 2. The apparatus must be placed where no other light sources can interfere with the experiment such as in a dark-room. 3. Switch on the bulb (initially use a 20W one). Allow 5 seconds before taking a reading. This gives the filament time to fully heat up, so the bulb is at maximum intensity. 4. Record the reading on the Voltmeter.

Repeat step 3 for bulbs of 40W, 60W and 100W. Record the reading for these also. 5. The entire experiment should be repeated twice more in order to ensure consistency in the results. 6. Plot a graph of the average of all 3 results. Results Wattage of Bulb V1 V2 V3 Average 20 The highlighted result is the only one I see as anomalous. See over for graph. Graph of Various Wattage bulbs against the resistance of an LDR.

While not exactly a straight-line graph (for reasons I shall explain later), we see the general principle that the voltage is increasing with the wattage of the bulbs. Evaluation As you can see on the results table, I have highlighted an anomalous result. Assuming that the apparatus was assembled correctly and that I read the results accurately from the Voltmeter, the resistance of the LDR may have been affected by other factors. Resistance can vary with temperature; in fact it increases as the temperature rises and vice versa.

It may have been that the current flowing through the circuit was sufficient enough to raise the temperature of the resistor, due to the massive number of electrons flowing down such a thin wire. If this was so, then as the experiment progressed, the resistor would have become hotter, increasing the resistance and therefore biasing the results. Were I to repeat the experiment again, I would need to make sure the temperature of the circuit was constant to prevent this factor from biasing the results. This could be done by replacing the resistor with another of identical resistance or by allowing one resistor time to cool down between readings.

Furthermore, if the light intensity of the bulbs was not a constant throughout the experiment, this would have also affected the resistance of the LDR. We must not forget that these light-bulbs were powered from the Mains AC supply, which has an average voltage of 235V. Depending upon the power consumption on the local grid, the voltage supply may have varied; this would have affected the light intensity. To solve this problem, a more stable power supply is required. It is also worth noting that we do not know that all of the light bulbs were emitting the same range of frequencies.

We assume that there is a certain frequency of light which will provide the correct amount of energy for an electron to move from one electron level to another. We also assume that the light-bulbs all contained this particular frequency of light and all the electrons were responding to it with every single bulb. This assumption is unsafe. We have no guarantee that the electrons in the LDR were all responding to the same frequency of light. If the frequency varied, then the amount of energy transferred to the electron would have varied, increasing or decreasing its potential to carry charge.

To solve this problem all the frequency spectrum intensities of the bulbs need to be measured before the experiment to make sure that the spectrum of each bulb was identical. Conclusion Through careful examination of the results table, graph and of my explanations, I think we can safely say that the voltage across an LDR will increase when the intensity of light at a certain frequency increases. This ties in with my initial prediction that the voltage would increase with the wattage of the bulbs. Had I more time I would like to examine the voltage across the LDR when exposed to lights of different frequencies i.

e. all the colours in the spectrum. Since we know the frequencies of all the colours of light, it would be possible to prove a definitive link between light frequency and the amount of energy transferred. If we wish to talk about the Quantum aspects of this experiment, this experiment goes a long way to prove that light has particle-like properties as the amount of energy needed to make an electron move from one level to another is fixed and yet the light seems to provide this exact amount every time it falls on the atom.

Essentially, the electrons are receiving a certain amount of energy each time. It could be that every single light ‘wave’ contains an identical amount of energy or it could be true that single photons are delivering an exact ‘packet’ of energy to allow the electrons to become Charge carriers. Page 1 4/30/2007 Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section. Download this essay Print Save Here’s what a teacher thought of this essay 4 star(s).

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• University/College: University of Arkansas System

• Type of paper: Thesis/Dissertation Chapter

• Date: 13 October 2017

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