Or in our case,
F ∞ 1 / r2
Substituting F for d,
d ∞ 1 / r2
To turn that into an equation and not proportionality, we must insert some sort of constant,
d = k / r2
This makes sense. If the objects have a greater charge, and thus have a great excess or deficit of electrons, they will have a stronger force of attraction or repulsion with the other object. Similarly, the closer the objects are together, the more unstable the electrons become and thus tend to increase the stronger force of attraction or repulsion between the objects.
Variables
With regards to what was held constant throughout this experiment we must consider that the size and weight of the pith balls, the length of the string, and the charges given to the pith balls were the same. It was quite difficult to assign both pith balls the same charge, although we assumed Q1 was equal to Q2. The method we used to charge them, friction by means of a cloth and acetate strip, is almost impossible to measure.
Throughout each of the five trials nothing was changed as we simply wanted 5 identical trials. The distances d and r changed but not due to our modifications
We had to measure each time both the distance between the balls, and the displacement of ball A from its original position. This was done with the help of a mirror and ruler located behind the hanging ball.
Data Collection:
Data Table 1 – Positions of pith balls
Data Analysis:
Data Table 2 – d, r, and 1/r2
The method used to calculate the value of k is simple;
isolating the k gives,
Conclusion:
Evaluation:
It must be said that this experiment was indeed an experiment of speed and concentration. The amount of time we had before the electron charges leapt off the pith ball or the acetate strip was incredibly small. This problem was magnified by the fact that Belgium is indeed a very wet country, that at a time like this is hardly ever dry and it makes it harder for the charges to stay on the pith balls. Moreover there were several difficulties at the start of the experiment with regards to how quick and how long to use the cloth to charge the acetate strip. It became very frustrating after rubbing the cloth on the stick for a long time only then to lose the charge by not being quick enough to get to the ball.
We attempted to keep our accuracy as high as possible but at times it was simply too hard because the distances that the ball at times moved were millimetres and our eyes from so far away could only really be accurate to the centimetre or centimetre and a half. Furthermore, it appeared at the start of the experiment that the balls were actually attracting as a pose to repelling. This then turned out to be a mistake in procedure and those results were neglected but nonetheless time was lost. As I mentioned before, the sheer speed at which this experiment must be done contributed greatly to the source of error and can be held accountable for the not so perfect relationship.
With regards to what can be done to better/improve this experiment, not much can be said. It would be very hard to charge the balls more by use of cloths and friction, and no other appropriate measuring device other than your eyes and a ruler can be valid. Perhaps the best option left is to simple get more trials, as many as possible, because this should average out the final result to a better figure – if done correctly.
