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Comparing and improving two rainfall gauge experiments.

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AS Physics Practical; Comparing and improving two rainfall gauge experiments The aim of this experiment is to test and improve an existing rainfall measuring experiment using a potential divider. I have done this by modifying the equipment I use; this has given me a better resolution and more linear results. Apparatus For the first unimproved experiment * 5 volt Dc power supply * Rotary potentiometer * Float * Voltmeter * Beaker * Metal rods * Blue tack * Clamp stand * Ruler For the second experiment; * 5 volt DC power supply * Rotary potentiometer * Clamp stand * Arm with joint * Volt meter * Beaker * Float * Ruler Safety If the water is spilt then it must be mopped up. The beaker might break if it falls on the floor therefore all equipment must be kept away from the edge of the table. The rotary potential divider must be secured in a clamp stand. This must be held tightly so that it will not fall on the table as this would damage both he table and the rotary potential divider. Diagram of Experiment 1 Diagram of Experiment 2 Theory A rotary potentiometer has a primary use in fuel gauges in cars however it is also useful in rain detectors or robot arm sensors. It works because, when a 5 volt current is passed through the two potential divider connections and the rotary arm if fully opened up the full current will pass through. ...read more.


To stop this from happening in the second experiment I used an arm that had been professionally made this meant that it gave accurate results because it would be at a constant angle of 70�, and did not twist or hit the side. The two arms where attached between the 70� angle with two plastic disks these where on a pivot to allow the arms freedom to move from left to right of each other however it would not spin in the opposite direction. This spin would give the anomalous results. For the first experiment, the ping-pong ball also caused problems. When water was added to the container the ball did not rise this was because it had holes in the surface and therefore filled with water. To stop this occurring I changed the ball. In the second experiment, I changed the ball to a polystyrene ball, I did this because polystyrene floats better than a PVC ball, and this gave my results for the second experiment an extra degree of accuracy. The second experiment also had fewer problems as it was an improved experiment. At first when I set, the second experiment up the potential divider was faulty therefore; I had to change this for a different rotary potential divider. In addition, my first selected beaker for the second experiment also made the float hit the side and gave me faulty readings this meant I had to change for a slightly larger beaker. ...read more.


Before if the first experiment were left for 24 hours the float would have hit the side if it floated at all, and there would have had to be 3mm of rain for a clear reading to be taken. With the improved experiment, it could now be left outside, because the new arm joint allows the arm movement and to measure at a constant angle however, it will not hit the side of the beaker, only 2.5mm of rain would have to fall for a reading to be taken and the ball is assured to float. If I was to improve the experiment further, I would use a resistance box, and a power supply that gave a constant 5 volts instead of a power supply that gave a fluctuating 5 volts, I would also use a more sensitive voltmeter. A resistance box would not increase the resolution however; it would increase the strength of the signal to the voltmeter and therefore giving a better reading. If I were to use a fixed 5 volt, power supply it would give me a constant 5 volts instead of fluctuating around 5 volts this would also improve my voltmeter readings and linearity of my graph. If I was to use a more sensitive voltmeter I could increase the accuracy of my results by 1 decimal place this although would not improve my results it would make them easier to anomalies and then I would be able to find a more affective way of stopping the anomalous results. ...read more.

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