Name: _______________________________
Period: _____
Charges and Fields – Tech Lab
Part 1: Charges
Everyone is familiar with the somewhat painful implications of electrostatics. After quickly shuffling
across the floor we accumulate a charge. Often, the first we know of this development is when the
charge rapidly leaves our body through contact with another object. Charging by contact (and the
ultimate discharge) is humorously portrayed in the following simulation starring John Travolta.
Go to: http://phet.colorado.edu/en/simulation/travoltage
Have fun zapping JT. Then answer the following questions:
1) Describe the charge distribution on JT prior to discharge. (How much charge is there? Where is
it located?)
2) Compare charging and discharging. What is the biggest difference?
3) Based on this observation, infer why discharge is often accompanied by pain, but charging is
seldom even noticed.
4) Observe discharges at several arm positions. Suggest a relationship between arm location and
charge accumulation? Evaluate the extremes to provide reasoning. In other words, at what
positions does discharge occur nearly instantly and at what positions does discharge not occur?
5) A standard electrical outlet will provide a voltage of 110V and is capable of killing a person. A
shock from static electricity can be measured in the tens of thousands of volts and seldom
results in more than an annoyed sibling. Attempt to explain this phenomena using the terms
voltage and current.
Go to the following website and click “Run Now!” to begin the simulation.
http://phet.colorado.edu/en/simulation/balloons
1.
Practice collecting charges from the sweater by moving the balloon over the sweater. What
kind of charges will the balloon collect? _________________ This indicates that the balloon is
picking up what type of particle? ___________________
2. Once your balloon has gathered a quantity of charges, move it to the right away from the
sweater and let it go halfway between the sweater and the wall. What happens to the balloon?
________________________________________ What makes it move the direction it moves?
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3. Now move the balloon so that it is closer to the wall (without touching). What do you notice
about the charges in the wall?
Charges and Fields Tech Lab
______________________________________________________________________________
______________________________________________________________________________
Let go of the balloon before you get to the wall. Describe the motion of the balloon. Is it
different than #2? Why?
______________________________________________________________________________
______________________________________________________________________________
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4. Finally, move the balloon so that it collects all of the charges from the sweater. How does this
affect the motion of the balloon when it is released in the middle again? Does it affect speed of
motion, distance of affect, etc.?
______________________________________________________________________________
______________________________________________________________________________
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5. Push the reset all button. Click on the two balloons button. You should now have a blue and a
yellow balloon. One at a time, move the balloons over the sweater to collect charge. What type
of charge do they collect? _________________
6. Now move both balloons to the center between the sweater and the wall. What happens when
you try to put the two balloons in the center between the sweater and the wall?
______________________________________________________________________________
______________________________________________________________________________
Conclusion Questions:
1. What type of charge was transferred from the sweater to the balloon?
2. What type of charge did the sweater have at the beginning of the experiment?
3. What type of charge did the sweater have at the end of the experiment?
4. What type of charge did the edge of the wall have before the experiment?
5. What type of charge did the edge of the wall have when the balloon was brought near it?
6. What type of charging is taking place when the balloon is charged by touching the sweater?
7. What type of charging is taking place when the wall is charged before the balloon touches it?
Charges and Fields Tech Lab
Part 2: Electric Fields
Go to the following website
http://www.falstad.com/vector3de/
1. Click the “charge” dropdown menu and select “point charge double.” Click the “Display:
Particles” dropdown menu and select “Display: Field Lines”. This shows a 3D animation of the
electric field of two objects that have the same charge. Draw a 2D sketch of the field below:
2. Change the first dropdown menu (“point charge double”) to “dipole”. This shows a 3D
animation of the electric field of two objects that have opposite charges. Draw a 2D sketch of
the field below:
Part 3: Electric Field Hockey
Go to the following website and click “Run Now!” to begin the simulation.
http://phet.colorado.edu/en/simulation/electric-hockey
The objective of this game is to get the black “puck” into the goal. The puck is positively charged, so you
can cause it to move by placing + and – charges that are in the top right of the screen.
1. Check the box next to “Field” in the bottom right of the window.
Charges and Fields Tech Lab
2. Place some charges to “aim” the puck towards the goal. When you are ready, click “Start” to
release the puck. To try again, click “Reset.” To clear the field of all charges, click “Clear.” Next to
the “reset” button, it tells you how many “tries” it has taken you to beat the level. Next to the
level selection, it tells you how many “charges” are on the field.
3. The buttons in the bottom left show what ‘level’ you are on. When you beat the practice level,
select “Difficulty 1” which is a bit harder. Try to beat all of the levels.
4. Below, state if you beat the level and write down how many “tries” it took to accomplish it, as
well as how many charges you used.
Level
Did you beat it?
# of Tries
# of Charges
Practice
Difficulty 1
Difficulty 2
Difficulty 3
Conclusion Questions:
1. Which direction do electric field lines point for positive charges?
2. Which direction do electric field lines point for negative charges?
3. What do the direction and strength of the field lines indicate for the (positively charged)
“puck?”
4. Does the (positively charged) puck always move in the same direction as the field lines it
was passing over? Revise your answer to question three if needed!
5. What happens if you changed the charge of the puck from positive to negative?
Charges and Fields Tech Lab
6. What happens when you increase the mass of the puck?
7. How did the distance between the puck and the particles affect the force of the puck?
8. If someone were to tell you that the force of the puck is inversely related to the distance
between the puck and a charge, would you agree? Explain.
9. When attempting to score on difficulty 3, you may have noticed how difficult it is to
succeed without manually moving charges as the simulation is running. Is the puck
acting the way you want it to all the time? Explain why it can be difficult to score.