It also helps to cancel out any other light, which will obviously get in the way more, the further the LDR is from the bulb. I will find out how much this effects the results in the preliminary practical. I will needed to keep the bulb at a set height, perhaps 2cm above the LDR. During the preliminary practical, there are many things I can do to get the optimum results. That includes keeping the distance and height the same, but also taking the correct resistance reading. You can set the resistance readings on the Multimeter to different levels of accuracy. If you dont have a large enough setting, the dial will display one.
I will then go down one until I get a suitable answer. I may even have to change the accuracy settings during the preliminary practical, if they become too inaccurate. My independent variable is voltage (potential difference). I will be finding out how the intensity of the light effects resistance of the LDR. I will be going up in gaps of 2 volts, up to 12 or 14 volts, giving me seven readings. I need to make sure I get two, preferably 3 sets of good results, to iron out anomalies, getting a better overall average. Some small errors could creep in when reading off the Multimeter. The resistance readings will start to fluctuate slightly.
I will take the best reading I can by waiting until the Multimeter stays on one number. The more accurately I set the Multimeter, the harder this is to do. Of course, this is only an initial method. The preliminary practical will give me a good feel of the equipment, and where things could go wrong. I will be able to change things for the final practical. Preliminary Work I will need to undertake a preliminary practical for many reasons. A preliminary is very good for helping me get a feel for the equipment. I will do it to find out how much resistance there is without the lamp being turned on, to see what effect other light has on the LDR.
I will also see if this changes when the LDR is out in the open. From this, I can decide where I will put the LDR in the final experiment. To start with, I will have the LDR directly under the lamp, so as little light as possible gets to the LDR. A second thing I will probably do, is slowly increasing the voltage until a noticeable difference is shown on the LDR. I will also get a good feeling of what I expect to happen in the actual main practical, and where I will be getting anomalous results. I may also be able to predict trends, and alter my graphs. I will only take readings at a few voltages.
I may take readings at 4 volts (the lowest reading), 8 (a middle reading), and 12 (the highest reading. These are all of some use, as they will give me an estimate of the trends, and by finding the highest and lowest readings, the range. I will also need, in my preliminary practical, to take down the conditions that the practical is taken in. I will need to make the experiment as fair as possible, so I will need to see where all the extra light is coming from, so I can regulate that in my main experiment, and also things like the vertical distance from the LDR to the lamp.