Part I - Simple observations:

1. (a) Adjust the distance between the particles to 10 pm (picometers) using the distance widget. Then use the up/down widget for each particle to set the charge on both particles to +1 and record the magnitude of the force acting between the particles in the table above. Also, record the potential energy and note whether it is positive or negative. (b) Then increase the charge on one of the particles to +2 and fill in the second row in the data table. (c) Now increase the charge on the other particle to +2 and record the results above.

Summarize:

i. What is the effect (on the force and potential energy) of doubling the charge on just one particle?

ii. What is the effect of doubling the charge on both particles?

2. (a) Return the settings of charge to +1 on both particles. Then increase the distance separating the particles from 10 pm to 20 pm and add a new row to the table above. (b) Now decrease the distance to 5 pm and fill in another row.

Summarize:
i. What happens to the force acting between the objects if the distance is doubled?

ii. What happens to the force if the distance is halved?

iii. What happens to the potential energy? Does it change proportionately with the force when the distance is doubled and when the distance is halved?

3. Repeat part (a) of number 1 above except set the charge on both particles to -1 instead of +1. Record the results in the table.

i. How do the values of force and potential energy compare with those you recorded in 1(a) above?

NOTE: If the charges on the particles have the same sign, the force is repulsive and it tries to push the particles apart.

4. Repeat part (a) of number 1 above except set the charge on one particle to -1 and the charge on the other particle to +1. Record the results in the table.

i. How do the values of force and potential energy compare with those you recorded in 1(a) above? What is the sign of the potential energy?

NOTE: If the charges on the particles have opposite signs, the force is attractive and it tries to pull the particles together.

5. Finally, set the charge on one of the particles to zero (neutral) and set the other charge first to +1 and then to -1. Add the results to your table.

i. In either case is a force observed? What is the potential energy

Part II - More careful analysis of the effect of distance.

1. Explore the attractive force by setting the charge on one particle to +2 and the other to -2, then create a data table in Excel with distance for the x-variable and potential energy for the y-variable. Start with the distance at 5 pm and increase it in increments of 5 pm for each data point until the distance reaches 95 pm. Use your data points and the ‘scatter plot' option to build a graph with distance on the x-axis and potential energy on the y-axis. Label your axes appropriately, then print it and include it with this exercise. (Alternatively, you may create the graph on graph paper accurately by hand.)

From your graph:
i. What is the largest possible (maximum) potential energy that could exist when oppositely charged particles interact with an attractive force? At what distance would the potential energy reach its maximum? (Recall that with negative numbers, smaller is bigger, e.g. -2 is greater than -5.)

ii. What is the lowest possible (minimum) potential energy that could exist when oppositely charged particles interact? At what distance would the potential energy reach its minimum?

iii. How might the graph be different for a repulsive force acting between particles with charges having the same sign? What would be the maximum and minimum potential energies possible?