Lab 3 Electrostatics with Aluminum Balls

The previous portion of this lab has prepared you to generate and transfer a large charge, so that the initial Aluminum ball separation distance is sizeable. Since each charging process strips a different number of electrons, another method is introduced to make more quantitative measurements.

3.1 Goals

  1. Make a more accurate measurement of the transferred charge \(Q\) by making both Aluminum balls equally large, so that upon charge transfer, each ball carries the same amount of charge.
  2. Neutralize one Al ball, while the other keeps the charge \(Q\). Upon touching each other, the charge is split evenly again, so that each Al ball carries \(Q/2\). Repeat to ever smaller charges.

3.2 Prediction

see part A.

3.3 Procedure

  1. Use the previous results of mass and string length;
  2. Affix the two strings in a single point, such that the two Al balls touch each other;
  3. Maximally charge the PVC rod;
  4. Measure the separation of the charged Al balls;
  5. Remove the charge from one of the Al balls by grounding it (using your hand), and have the spheres touch each other. If the initial charge was Q on each Al ball, it will be Q/2 afterwards. Through repetition, you can achieve Q/4 and possibly Q/8, which is possible, but requires experience.
  6. Compute the relative error between expected Q/2 charge (based on Q measurement) and measured q/2 charge; repeat relative error calculations for Q/4 and Q/8
  7. Repeat procedure to make more precise measurements.

3.4 Measurement

Create a table with columns similar to this table. Note that you can compute the string angle \(\theta\). Here \(Q\) refers to the transfer charge and \(q\) is the calculated charge based on your model.

3.5 Graph

Make a graph of the charge \(Q\) versus the separation distance \(r\). Add your measurements from one run with several measurement values of \(Q\), \(Q/2\), \(Q/4\), etc. using dots. Then, add a curve with the predicted function \(Q(r)\) from the first lab part.

3.6 Discussion

Share the value \(Q/2\) derived from the first charge measurement and \(q/2\) from the second measurement. Also, report the separation distance and always include the appropriate units. Discuss where the charge went, when you grounded the Al ball. How does your measured value compare to values from the textbook? Does your model of electron transfer work? Is any mass transported?

3.7 Summary

Report the number of electrons N and the charge Q that you can remove. Describe your model of the atom. Comment on the behavior of charge and separation distance. How valid is your model? What is the connection of these results with Coulomb’s Law?

3.8 Additional Reading