Coulomb’s Law Lab

Aim:

        To investigate Coulomb’s Law by balancing the electrical force with other forces that are easier to measure and to show that the force of attraction/repulsion between two charges is inversely proportional to the square of the distance between them.  

Hypothesis:

        My prediction for this experiment agrees with Coulomb’s Law in the sense that I think there will be a clear relationship between the force of attraction and the distance between the two charges.  

        There is a logical explanation for this, take into consideration Figure 1.  

We can see that,                         

sinθ = d∙L.  

Also we can notice that,                 

Fe = m∙g∙sinθ.  

Combining these two equations, we get,

 F/m∙g = d/L  

or F = m∙g∙d / L

Keeping in mind that g and L are constant, we know that F is proportional to d (F ∞ d).

        Furthermore, we have the relationship

                                F = kQ1Q2 / r2

        Or in our case,

                                F ∞ 1 / r2

        Substituting F for d,  

d ∞ 1 / r2

Trial

Position of pith ball B

Original position of pith ball A

Position after repulsion

1

0.022 m

0.047 m

0.049 m

2

0.024 m

0.047 m

0.049 m

3

0.026 m

0.047 m

0.050 m

4

0.028 m

0.047 m

0.050 m

5

0.030 m

0.047 m

0.051 m

6

0.032 m

0.047 m

0.051 m

        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.