Electrostatic Lab Simulations Part II:  The Electric Field
Directions:  Open your web browser to: http://www.hinsdale86.org/staff/jliaw/.  Go to Explorations / Electricity & Magnetism / Electrostatics / Electrostatic Lab Sims Part II.  You will need to have Shockwave & Java installed for some of the sims—if it’s not installed on your machine it will automatically install itself or follow the link. 

Answer the questions below & make sketches as appropriate (a picture is worth a thousand words!); if necessary consult your textbook for extra help.  If you have trouble getting to the websites, try the Red Devil drive.

Defining the Electric Field:    
1.      In terms of the electric field produced by a charge, why does "it take one to know one"?
2.      In the animation the electric field source (“stationary”) charge is _____________.
3.      A test charge is moved into the electric field. How does the force on the test charge relate to its distance from the source charge? How much force on the test charge do you think there might be if the distance of the test charge were zero (contacted the stationary charge)?
4.      How does the simulation show the strength of the electric field on the test charge?
5.      How does the simulation show the direction of the electric field on the test charge?
6.      What is the charge on the test charge? (+ or -) __________
7.      Is the electric field intensity a vector quantity? _________ 
What two equations allow you to calculate the electric field intensity?

Electric Field Mapping Rules:  
1.      When using a “vector arrow” to describe the force a positive test charge would feel in space, what does the length of the arrow represent? What does the direction of the arrow represent?
2.      Why are field lines used instead of arrows to represent electric fields?
3.      If the “source charge” is negative, then what direction do electric field lines go? It it’s positive, then what direction do electric field lines go?
4.      How can you tell where an electric field is strong (or weak) by reading electric field lines?
5.      Where is the electric field the strongest: Near the source charge or far from it? How can you tell?
6.      Beginning with the letter “P”, how are field lines shown leaving or entering the surface of a test charge?
7.      What rule must be obeyed about the crossing of electric field lines? What incorrect fact would breaking that rule imply? 

Electric Field Line Modeler:  

1.      Set the modeler to medium resolution. Try the following charges and sketch the following 6 fields below and summarize the effects of: (a) charge (3 compared to 1, use the word “density”) (b) Both charged positive compared to both negative:

Q₁ = 1, Q₂ = 1                                                                         Q₁ = -1, Q₂ = 1

Q₁ = 3, Q₂ = 3                                                                         Q₁ = -3, Q₂ = 3

Q₁ = -3, Q₂ = -3                                                                       Q₁ = -1, Q₂ = 1

Conclusions:

(a)    Effects of charge: (3 compared to 1, use “density”)? 

(b)   Compare when both are charged positively to when both are charged negatively and does this difference depend on whether there is a big charge (3) or a small charge (1)? 

Visualizing Electric Field Lines:   http://www.falstad.com/vector2de/  OR  http://www.falstad.com/vector3de/

1.       Choose Setup:  point charge.  Try using your mouse to rotate the field view as well as adjusting the Field Strength and Number of Particles.  Make a sketch of the initial situation below and indicate the direction of the test particles flowing with arrows.  What is the sign of the point charge?  How do you know?  What happens when you choose reverse?

2.       Now choose Setup:  dipole.  Try using your mouse to rotate the field view as well as adjusting the Field Strength and Number of Particles.  Make a sketch of the initial situation below and indicate the direction of the test particles flowing with arrows.  What is the sign of the each point charge?  How do you know?  What happens when you choose reverse?  Try exploring other field shapes under Setup!  J
 

Electric Field Hockey:  Very Phun! :)   
 

1. Put your knowledge of electric fields to the test!  Play hockey with electric charges!  Place charges on the ice, then hit start to try to get the puck in the goal. Hints:  Select View to see the electric field. Pick Trace to see the puck’s motion. Make the game harder by placing walls in front of the goal as you increase the Difficulty!  When you figure out your highest level of Difficulty (at least 2 or 3), make a sketch below of your “solution” of charges to get the “puck” into the goal!

COOL STUFF:  Electric Field Simulator

Check out UTSAV.COM's Electric Charge simulator....try putting out some negative and positive charges in the field....watch out for collisions that will "neutralize" your charges!

CHALLENGE:  Can you create a field of charges to "trap" a positive test charge?