Physics Lab Worksheet


Determine how many electrons are transferred when yo rub a balloon on your hair

Main Idea

Create static change or two balloons Measure theelectricforcebetween the balloons Determine how many electrons were transferred to each balloon

Experimental Implementation

Electricforcewillberelatedtotheangle0 which istheangle at which the balloons sit in equilibrium


Analyze the free bodydiagram to relate the electric force to experimentallymeasurable quantities This processwill bethe same as 06 on A082 Equate the electric force from the free bodydiagramto the electric form from Coulomb’s law You can now solve for the numberof electrons N


Theballoons must be statically changed and freelysuspended i e the balloons need to be free to move apart Some practice will be required to achieve a stableconfiguration We will assume the balloons are equally changed Make sure you use an experimental procedure that willachieve this It is upto you todetermine exactly what to measure to achieve your experimentalobjective andhowyou willperformthese measurements One hint you will need to determinetheangle0 drawn above but it is easier to calculate the angle E using lengthmeasurements and trigonometry than it is to measure 0 directly


Maximum Score: 12

1. [1] Attach a picture of your experimental setup.

2. [2] Draw a free body diagram of the balloons in your experiment. Ensure that all relevant parameters are labelled.

3. [2] By analyzing your free body diagram, and using Eqs. (1) and (2) in the lab description, determine a “working equation” for this experiment. In other words, your goal in this experiment is to determine ???? defined in Eq. (2), and therefore you need to work out an equation that will relate ???? to parameters you can measure in your experiment.

4. [1] What steps did you take to ensure that each balloon acquired the same amount of charge?

5. [2] List the quantities you measured in your experiment and their values. The variables chosen

should match the labelling in your free body diagram.

6. [1] Show a calculation of ???? using the equation you determined in Q3.

7. [3] Comment on your value of ????. Is your value surprising, unsurprising? Does it seem reasonable upon further consideration? How could you verify if your result is reasonable? What do you think are the biggest sources of uncertainty in your measurement? How would you improve the experiment if you did it again?

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