Finding the Spring Constant of a Copper Spring Using a Potential Divider

        There are three wires that attach to the potential divider. The two outer ones are connected to a 2V cell and the centre wire connected to a voltmeter. Everytime I add a 1N weight I will calibrate the potential divider to 90°. To make this more accurate I will use a spirit leveller to get the potential divider pointer as near as 90° as I can. I will only use upto 10N because the spring may snap or even touch the surface. I will do the experiment twice so that I can draw error bars on my graph.

        

4.1 Diagram 1

        This is the circuit which I made up to do my experiment with.

4.2 Diagram 2

4.3 Diagram 3

4.4 Safety

        Wear goggles when handling the springs to protect your eyes. This will stop the spring recoiling and damaging your eyes.

4.5 Fair Test

• Length of wire – keep length of wire the constant to make sure this variable doesn’t affect the experiment.

• Cross sectional area – if the thickness of the wire changes then the resistance would change. The thicker the wire the less resistance there will be. This is another variable that will remain constant.

• Type of metal – throughout the experiment I will use copper wires. If I used different types of wires then the results wouldn’t be reliable as different types of wires let through different currents at different rates.

• Temperature – the higher the temperature, less number of electrons passing through the wire.

5.0 Results

Here are the sets of results that I recorded from my two experiments. They show the voltage changing through the potential divider at different forces.

Test 1

Test 2

        Now I have got all the information that I need I will now construct a graph of force against voltage.

6.0 Graphs

7.0 Conclusion

        I successfully constructed a sensor that enabled me to take accurate measurements. The results that I obtained from the experiment were limited this was due to the fact that I didn’t have the adequate equipment to build my sensor with. If I had an inbuilt  spirit leveller then it would be more accurate to calibrate the sensor. I didn’t have this so my results may be slightly off what they would be it I had inbuilt spirit leveller. However I was able to collect quite accurate and reliable results as I did the experiment twice. The resolution of my sensor is the smallest change in the quantity it can measure. The resolution of my sensor will not be as good as a well-constructed sensor because I am restricted with what materials and components I can used to measure this. My figures that were recorded on the voltmeter did not fluctuate so this means that the resolution was precise.  

        I have successfully completed my objectives because I was able to construct a test sensor. I have discussed the characteristics of the sensor and I was able to calibrate the sensor. I calibrated the sensor by keeping the potential divider marker at 90°, using a spirit leveller to judge when I had turned the marker to 90°. My sensor could be used as electronic weighing scales. Instead of adding the weights and calibrating the sensor I could hang an object off of the spring and take the voltage off of the voltmeter. I would be able to look at the voltage on the graph and look across to the line and see what weight the object was.

        

8.0 Evaluation

        From the material I was able to use to make the sensor, I made full use of the apparatus to make a rather accurate device. A built in spirit leveller would make my device more accurate, but I was able to use the sources that I was supplied with. The experiment went well and didn’t take me too long to complete it as I knew exactly what I was going to do before hand. I don’t think that I should add anymore than 10 weights if I did the experiment again as the spring would snap. Next time I will have to think of a better system to calibrate the sensor to get an even straighter line on my graph. By doing this the marker on the potential divider will be closer to 90°.