PhET Simulation: Coulomb’s Law, Study notes of Physics

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PhET Simulation: Coulomb’s Law Dhiraj Maheswari Laboratory 1

Purpose : The purpose of this laboratory is to learn the concept for Electric force and Coulomb’s law. Learn how the magnitude and sign of charge affect the Electric force. Determine the effects of distance on the charges and how it affects the electric force. Introduction : Coulomb’s law describes how like and unlike charges attract or repeal each other. Similar charges like two positive charges will repeal each other. While two dissimilar charges will be attracted to each other. The law calculates the magnitude of the force between the two charges and the distance between the two points. These electrostatic forces of repulsion and attractions can be very strong when the two points are close regardless if the force was an attraction or repulsion. However, as the distance between the charges grows larger, the value of the electrostatic force drops. Procedure : The experiment was completed through the PHET simulator for Coulomb’s law. Data and Data Evaluation : Include the entire lab activity packet and any tables or graphs created during the experiment. Data should consist of as many trials as indicated in the instructions. The units for physical measurements (kg, m, s, etc.) in a data table should be specified in column heading only. PART 1: DATA COLLECTION Once you are in the simulation, which looks like the image below, follow the instructions as you go through each question in order to work your way through the simulation and answer the questions.

 Click on the ruler and drag it up into the center of the red and blue “charges” so that you can line up the dashed lines more precisely with the ruler numbers.  UNCHECK Scientific Notation. TABLE 1: Changing Charge 1 Charge 1 ( μC ) Charge 2 ( μC ) Distance between charges (cm) Force (of 1 on 2) ( N ) Force (of 2 on 1) ( N ) Arrow direction (away or toward each other) 2 8 4 55.29 55.29 away 4 8 4 110.54 110.54 away 6 8 4 165.86 165.86 away 8 8 4 221.15 221.15 away 10 8 4 276.43 276.43 away TABLE 2: Changing Charge 2 Charge 1 ( μC ) Charge 2 ( μC ) Distance between charges (cm) Force (of 1 on 2) ( N ) Force (of 2 on 1) ( N ) Arrow direction (away or toward each other) -3 2 5 14.98 14.98 Toward -3 4 5 29.96 29.96 Toward -3 6 5 44.94 44.94 Toward -3 8 5 59.92 59.92 Toward -3 10 5 74.90 74.90 Toward

TABLE 3: Changing the Distance Charge 1 ( μC ) Charge 2 ( μC ) Distance between charges ( cm ) Force (of 1 on 2) ( N ) Force (of 2 on 1) ( N ) Arrow direction (away or toward each other) 9 -7 2 519.94 519.94 Toward 9 -7 4 235.86 235.86 Toward 9 -7 6 115.55 115.55 Toward 9 -7 8 69.90 69.90 Toward 9 -7 10 56.62 56.62 Toward PART 2: DATA ANALYSIS

1. Use the values from the second row of data in Table 2 and plug them into the equation for Coulomb’s Law to solve for the Force. Considering this to be the theoretical value, calculate the % error for this trial. Include your calculations and a screenshot, corresponding for these values from the simulator.

2. Plot a graph with Vernier Graphical Analysis using the values from Table 3. On the y-axis place the product of the charges q1 and q2, and on the x-axis place the squared distance between the charges.
3. Use the best fit option in the graphing tool and determine the shape of the slope. Insert the graph in the completed laboratory report and write your conclusions. Analyze the results in your tables and write your conclusions in the completed laboratory report.

Results and Conclusion : Table 1 observations : As the charges are both positive values but the distances remain the same, the only observation to be made is the force repulsion. In addition, the greater the charge, the greater the force of repulsion. Table 2 observations : The charges are attracted to each other because they are opposite values. Since the charges remain at the same distance, you see the force grow less as the charge value increase. Table 3 observations: The only variable that changes is the distance. Since the charges are of opposite values, they are attracted to each other. The closer the distance becomes, the force decreases. A percent error of 60% was reached when the values of row 2 were calculated into Coulomb’s law formula. It is not clear why the variation is so large but since it is a theoretical number that may play into a factor as to why the error was so large. It could also be that the calculations were computed incorrectly. However, the graph displays what is expected to be observed when the distance is increased between two points. The force attraction decreases as the separation grows larger. Conclusion: Although the calculations were not as expected in this experiment, the graph and table values are consistent with Coulomb’s law. Opposite charges are attracted to each other while similar charges are repulsed. However, the magnitude of that force is dependent on the distance between the forces, growing stronger as the charges come closer but greatly decreasing as the distance between the points grow.