This simulation shows a large metal conductor (in grey) that can be given many extra electrons. Play with the simulation for a few minutes and write down your observations.

Do you notice any difference between how the electrons move for the square conductor as compared to the circle conductor? Why do you think the electrons are behaving in this way?

Hint: Try this with a relatively small number of charges.

Now run the simulation several times (with either shape, but don't change it during these trials), keeping the "n-electrons" constant, but changing the "side-length" to different values several times. Record your observations about how the electrons behave as the side-length changes.

Throughout the questions above, you should have noticed that the electrons spread out and move to the surface of the conductor.  Why do you think this occurs? Additionally, summarize what patterns you observe when shape and electron number changes.

Now click on the "NetLogo Code" tab below the simulation.  Can you figure out a way to change the color of the conductor from grey to red? In order to test your solution, you will need to click the button, "Recompile Code."

Hint: you can type Ctrl-F to find all the places in the code where the word "grey" is used.  Maybe that has something to do with the color used? :)

Create 2 square conductors of equal size and with equal excess charge. Click setup and go, and then wait until the charge (mostly) stops moving. What do you notice about the arrangement of charges in each square?

Hint: you can increase the model speed using the slider at the top of the simulation.

Now touch the two squares together. What happens? Why do you think this occurs?

Set up 2 conductors (of either shape) with equal charge, but significantly different sizes. What happens to the electrons when you touch these two conductors together? Explain what the final arrangement of charges looks like and why it ends up this way.

Again, keep the size of the conductors the same and the initial number of electrons different. Touch the conductors together, and wait for the charges to stabilize. Below, record:

• How many electrons started on each object?
• How many electrons ended on each object?
• How many electrons moved?
• Is there a pattern or "rule" governing this behavior? Try another trial and see if your idea checks out...

There are three objects on the simulation -- the sweater, the balloon, and the wall. Would you characterize those objects as conductors or insulators? Why?

How do you expect charge to behave/move as a result?

Before moving anything (or click the orange reset button if you already have), what is the charge of each object?

Now bring the balloon near the wall. What happens macroscopically (big picture) between the wall and balloon? What happens microscopically (to individual charges)? Why does the balloon stick to the wall?

If the balloon was positively charged instead of negatively as it is in the simulation, would it still stick to the wall? Explain how this situation would be possible in terms of charge behavior and movement.

Take a few moments to explore this simulation. What do you think this simulation is showing?

What variables can you identify as dependent variables?

Conduct and run an experiment to determine the relationship between the charge of the first particle, charge_1, and the force.  Collect data points using the "Collect data point" button when the simulation is running. Change your independent variable at least 8-10 times to collect different values of the dependent force. Then, drag these variables from where they appear in the table to the correct axes on the graph, and CODAP will create a graph for you.  

Note: It is not necessary to collect multiple trials of each data point.

What type of relationship do you observe between force and charge_1?

Let's now find a mathematical relationship between charge_1 and force.  

Is this data linear? If so, we can click on the graph, then click on the ruler tool, then on the "least-squares line". This will draw a best fit line through your (linear) data. You can then write a mathematical model that describes the line. Remember to use the actual variables, not x & y, and to determine what the units must be for slope and intercept.  Write your mathematical model in the answer box.

If your original data was not linear, follow the procedure listed below the simulation to linearize your data with CODAP.

Upload your graph from the previous question by clicking on the camera icon to the right of the graph.

Conduct and run an experiment to determine the relationship between the separation of the two charges and the force. Collect data points using the "Collect data point" button when the simulation is running. Change your independent variable at least 8-10 times to collect different values of the dependent force. Then, drag these variables from where they appear in the table to the correct axes on the graph, and CODAP will create a graph for you.  

Note: It is not necessary to collect multiple trials of each data point.

What type of relationship do you observe between force and separation?

Now use your simulation and CODAP to determine write a mathematical model that describes the relationship between force and separation. Use the same process as you did in 2.3 above to linearize your data if necessary. Write your mathematical model in the space below.

Let's look at the three relationships we determined on the last page:

1. Force is directly proportional to both charge_1.
2. Force is directly proportional to charge_2.
3. Force is inversely proportional to the square of separation.

Knowing this, let's write one proportion that says how force relates to all three of these variables. 

Hint - we did something similar with Gravity not too long ago!

Now we are ready to find that constant of proportionality, k. Use the simulation to record one trial. Plug in the values of the force, both charges, and separation, and see if you can solve for k. We are looking for the value of k and also its units. Record your answer in the box below question 3.4.

In the last section, we found a value for the proportionality constant k. This number has to be programmed into the code somewhere.  See if you can find what line of code the value for k shows up. 

What line (#) of code defines k?

Hint: if you skipped the directions above, click on the dropdown button labeled NetLogo Code...

The most important thing our program does is actually calculates the value of the electric force interaction. Look through the code to see if you can find where this takes place, and then copy/paste the line(s) of code that calculates the electric force.  

Hint: NetLogo uses the command "set" to store a value. For example, if I wrote set answer 3 + 4, the variable "answer" would hold the value "7".

Drag a yellow dot out of the box at the bottom labeled "Sensors" onto the grid. Drop the sensor on the page. Then click and hold the mouse button down to drag the sensor around the charge.

What do you notice about the direction of the arrow at all times?

What do you think the arrow on the yellow sensor represents?

Place a sensor 10 (small) gridmarks to the right of the point charge. Now, place a second sensor 20 gridmarks below the point charge. Compare the length of the two vectors.

What can you conclude about the relationship between electric field strength and distance? Predict and record a mathematical model that describes the relationship between electric field strength and distance (it's okay if it's not correct yet!).

Place another +1nC charge on top of your original +1nC charge so that you have a +2nC charge in the center of the screen.

What happens to the strength of the electric field at the location of each sensor that you had previously placed? What can you conclude about the relationship between electric field strength and the magnitude (strength) of the point charge?

In what place or places is the field the strongest?

Check the box titled, “Electric Field.” What appears? What do these arrows represent?

You will find the field is weak far from the positive charges. Where else is the field very weak (even zero) in strength?

Describe as best you can the general direction of the field in the box below. Now, check the box on the simulation labeled "Electric Field." Were you correct?

Sketch what you think the field lines would look like in the area between the plates, as well as around the outside of the plates.

If you placed a positive test charge in between the plates, where would it move? Why?

Does the positive test charge move along field lines? Why or why not?

In the previous page, you brainstormed a few rules for how to draw electric field lines. Here are the rules physicists usually use to draw field lines:

• Field lines point away from positive charges, and towards negative charges, using an arrow to indicate direction.
• Field lines are closer together to show when the magnitude of the electric field is stronger, and farther apart when it is weaker.
• Field lines can't cross. This "Ghostbusters" Rule (don't cross the streams!) exists to show that there is one unique direction for the electric field (and therefore electric force) at each point in space.
• Electric field "lines" are actually smooth curves, but the Electric field at a particular point (and also the Electric force) is a vector tangent to the electric field lines.

What questions do you have about these rules so far?

Search for an image of the field surrounding two positive charges. How does your drawing compare to the image you found? 

The diagram below shows a solid metal conductor with electrons located on the surface, as we saw in Lesson 1 on charge interactions.

Using the rules we discussed, draw what you think the electric field lines look like outside the conductor due to the charges on the surface.  

The diagram below shows a solid metal conductor with electrons located on the surface, as we saw in Lesson 1 on charge interactions.

Using the rules we discussed, draw what you think the electric field lines look like inside the conductor due to the charges on the surface.

How did your field diagram for outside the sphere (Q6.5) compare to inside the sphere (6.7)? Does this difference make sense based on what you know about charge behavior from earlier in the unit?