From my Preliminary Study, I have discovered the appropriate distances that I will use in my final experiment.
As there will be 5 readings, there will be 5 different distances. 0cm will not be one of the distances because the LDR can't be put in to the Bulb.
We will keep small distances because of the external light entering from the windows of the classroom. The more the distance, the more external light will interfere. However we must have external light for safety reasons. Without external light, accidents could occur, which could result in bulbs or anything else dangerous breaking. This would be extremely dangerous as the broken glass of the bulb or anything else sharp can hurt someone.
My distances are as follows:
2cm, 4cm, 6cm, 8cm and 10cm.
I have used a smaller, less dramatic change in distances; I used 2-4cm rather than a jump from 2-8cm. This is because with a smaller change in distance, the resistance will be less and there will be less interfering of the external light with the experiment, making the results more accurate.
I will be doing 2 trials in the experiment, for the accuracy of the results. If my 2 trials are not within 10% of each other, then I will have to do a third trial for that particular distance.
I will keep my investigation a fair test by making sure the distances are measured accurately with a ruler. I will make sure that the brightness of the bulb and the power supply will always stay the same. There would be no light other than the bulb and external light for safety reasons.
Prediction
My prediction is that the bigger the distance, the bigger the resistance. The resistance increases because the greater the energy from light (bright), the more free electrons can move from the LDR. If there is less light, the numbers of free electrons are less; therefore the LDR becomes a bad conductor, increasing the resistance. Therefore the further away the LDR from the bulb, the more resistance, therefore less current will be recorded. The more electrons, the more current would be flowing through because the more electrons, the more strong successful collisions will occur, as there is more energy present (due to more light from the bulb).
I can also find out exactly how the distance affects the intensity (density of light). This can be done through the ‘Inverse Square Law’. The formula for the Inverse Square Law is:
The power (of original bulb) and 4 (distance) will not change. The only measurement that will change is the Int. = Intensity at distance from the light bulb.
The thing with Inverse Square Law is that if the distance doubles, the inverse intensity will be ¼. If the distance is 3 times more, then the inverse intensity will be 1/9th of the light, because of the distance being
Method
First of all using an ammeter, a voltmeter, a LDR, a bulb and battery; the circuit was built.
I made sure that the power supply was set on 12.
Then I switched on the power supply to see if the bulb and the battery are working.
After that, I accurately measured the distances on a piece of paper. The paper was a great help because it showed me exactly where my LDR should be placed.
At last the lights were turned off and we could start our experiment. The external light was still entering the room through windows for safety reasons. Without external light, a person can’t see where he is going and might bump into someone, damaging equipment and may be hurting themselves especially when handling with glass (bulb).
Then the LDR was placed in position and the power supply was switched on.
I noted down the result, and continued to do so for the rest of the readings. I took the experiment twice for every reading as there were two trial used for the accuracy of results.
When I finished the experiment I put away all my equipments very neatly and then started to find the average of the current.
The average current was then multiplied by 100 to convert the milliamps into amps (so that the resistance can be found out).
Then using the formula I found out the resistance.
Just before plotting the graph I squared the distances in order to use the Inverse Square Law.
The graph was plotted Resistance against Distance .
Apparatus
Power Supply
Bulb
Battery
Voltmeter
Ammeter
LDR
Ruler (measurements)
Analysis
I will be analysing how the intensity of light (brightness) affects the resistance in a circuit. In my result there was one major anomalous result; this may be because my measurements and experiments were carried out not entirely as fair tests. There are about two points which I would not exactly label as ‘anomalous’ because they are not as far from the line of best fit than the major anomalous result. I have just left them as points on the graph as they are not far enough from the line of best fit to be called ‘anomalous’.
The actual labelled anomalous result was not due to the fact that I had to repeat the experiment a third time because the two trials were in 10% of within each other. It was an anomalous result perhaps due to the fact that my experiment may have some fault in it. I might have not measured the distances accurately, or may be as the experiment lasted for two days, the LDR on the second day was different from the first one, bringing some difference to the result.
From my graph, I can see that the further away the distance of the LDR from the bulb, the more resistance is present. This is because the further the LDR from the bulb, the more free electrons can move making the current’s flow harder as resistance blocks the way.
This makes my prediction come true, as in my prediction, I stated that as distance gets bigger, so does the resistance. As the resistance increases, the particles take longer to collide with less energy resulting in less successful collisions. As there are less successful collisions, this makes the resistance increase as there is less current flowing through.
Obtaining Evidence
As I will be using the ‘Inverse Law Square’ rule for my graph,
I have also included the actual plotted distance.
In order for the ‘Inverse Square Law’ to work, I have squared
the distances.