The second electrostatic lab/activity uses a Van de Graff generator to introduce new aspects of static electricity and to reinforce the topics introduced during the Balloon Charges lab.
The objective of this lab/activity is to:
a) Introduce the following key concepts:
-Conductors and Insulators
-Charging by conduction
b) Reinforce the following concepts from the previous lab work:
-Attraction of unlike charges
-Repulsion of like charges
-Charging by friction
-Polarization of charge
-Charging by induction
What is static electricity and how do charged objects behave around each other?
This is done as a class demo, so only one of each is required: Van de Graff generator, plastic foot stool, tape, yarn/string, grounded discharge sphere, pie tins (5 or 6), plastic cup, Styrofoam packing peanuts, balloon, pie tin with yarn taped to top, and fluorescent tube light (16”), and other random stuff that your students will come up with.
Safety / Electronics Disclaimer - Check that there won’t be any student participants who have heart conditions and/or require the use of a pace maker. Any electronics should be removed before coming in contact with the VDG; digital watches, cell phones, insulin pumps, etc…
The Van de Graff works best with low humidity, but still can have decent results with moderate humidity. Pick the demo day accordingly. Before we begin the activity, students will read through the introduction to the VDG as a class. The instructor should take a moment and discuss safety. A quick mention of the difference between voltage and amperage and how the large voltages produced by the VDG are relatively harmless due to the low amperage. I use the analogy of a waterfall. The height of the waterfall is the voltage and the amount of water flowing is the amperage. I then proceed to dim the lights and shock the back of my hand for a few minutes to spark (ha..ha..) some interest.Part 1:
As you follow the procedure on the actual lab sheet, volunteers will be required for the first four situations. The first three volunteers should be reminded that if they follow the instructions they will be shock free… this sometimes helps in getting the more timid students to participate. Throughout all of these situations keep students standing on the plastic stool and stop them from leaning on the table with their waist while in contact with the VDG. Here are a few helpful hints for each situation:Situation 1:
Try and pick a student with straight blond hair that does not have any product (gel / hair spray) in it. If it all comes together, you get a nice spread of hair.Situation 2:
The idea is to dispel the belief that the hand being removed will be shocked.
Same as Situation 2, but now we are trying to dispel the belief that they will be shocked when they put their hand back on.Situation 4:
This person should have a decent idea of what they are getting themselves into. There are usually a number of students who have figured out what this demo entails and will be more than happy to participate. If the student pulls their hand off and you see a big sweaty palm print, have them put use the back of their hand when putting it back on. For a bit more of a shock, when they pull their hands away you can also touch them to ground the built up charge and produce a greater difference in charge.Part 2:
Each situation should produce an exciting result. Here are a few helpful hints for each:Shocking:
The discharge sphere typically comes with a VDG, but if you don’t have one they are easy to find (science catalogs) or make. It consists of a metal (conducting) sphere, insulating handle, connecting wire (from sphere to ground connector on VDG).
You should get some decent discharge and with the lights off it can produce a decent show, but the kids get pretty bored with it after a bit. I usually let students do this demo.Flying Saucers:
Stack the pie tins and turn the VDG on. It helps to tape the bottom one to the VDG. Dancing Peanuts:
Tape the plastic cup/bowl (really any insulated container) and put in the peanuts. Cereal, salt and pepper, hole punch remnants all work as well, but may be a bit messier.Floating Balloon:
Try taping it to different places on the VDGHairy Hat:
Make sure to tape the hat to the VDG or it will fly away. The hairy hat is made by taking a pie tin and taping yarn to the top. Try to space each yarn strand equidistant from each other. String, cut tissue paper… any thing light and flexible may be used. Light Saber
: The high voltage discharge from the VDG can excite gases (phosphor) in the fluorescent tube. Use a shorter fluorescent tube light if possible, the 48” tubes tend not to light up as well. Turn off the lights and hold the tube in the center. Bring the electrodes from on end near or almost in contact with the VDG. Hold the tube in various locations and compare the differences in brightness. For the brave instructors… you may want to hold onto the other electrodes, but the discharge can be painful. A metal plate can be held across those electrodes to reduce the jolt.
Randomness or Randumbness:
This is a great chance for students be creative. Give them a bit of time to ponder the possibilities and then take the best four. I typically get one two good ones and a bunch of ways to shock things.
Part 1: There is no real assessment for part one, the closure is completed as a class.
Part 2: Students will need to recognize the difference between attractive and repulsive forces for each situation and be able to explain why the phenomena took place and use the terms highlighted in the introductory section.
Answer Key or Rubric:
Charging by conduction is used to explain why there were no shocks during situations one, two and three. Highlighting that the difference in charge is the cause of electric discharge (shocking) is used to explain situation four. The attraction of opposite charges becomes so great that the air in between be comes a momentary conductor and charge flows.
Van de Graff Lesson Plan
| Situation||Electrostatic Force|| Explanation|
|Shocking||Attraction||The difference in charge between the VDG and the discharge sphere is great enough to cause an electric discharge (spark). The fact that the discharge sphere is grounded helps produce this large difference in charge. |
|Flying Saucers||Repulsion||The pie tins are brought in contact with the VDG and become positively charged by conduction. A force of repulsion caused the pie tins to be repelled due to their like charges. |
|Dancing Peanuts||Repulsion||The peanuts are brought in contact with the VDG and become positively charged by conduction. A force of repulsion caused the peanuts to be repelled due to their like charges. |
|Floating Balloon||Repulsion||A balloon brought in contact with the VDG through the string and becomes positively charged by conduction. A force of repulsion causes the balloon to be repelled due to their like charges.|
|Hairy Hat||Repulsion||The hairy hat brought in contact with the VDG will become positively charged by conduction. A force of repulsion will eventually cause each hair to repel each other due to their like charges.|
|Light Saber ||Attraction||The difference in charge between the VDG and the fluorescent tube sphere is great enough to cause an electric discharge through the tube gases |