ElectrostaticInquiryActivity
March14–17,2017
Name:
6.1Ihaveamodelforthenatureandflowofelectriccharge.
• Ihaveamodelfortheelectrostaticinteractionthatcausesattractiveand
repulsiveforcesbetweenchargedparticles.
• Icandescribetheaccumulationofstaticchargeusingthetriboelectricseries.
• Icandescribehowasystemcanbecomeelectricallypolarized,andhowthis
allowsattractionbetweenelectricallyneutralobjects.
• Icanidentifyanddescribethebehaviorofconductorsandinsulators.
• Icandescribeandworkwiththefundamentalunitofcharge,andam
continuingtopracticewithscientificnotationusingpracticalunitsofcharge
suchasmC,μC,andnC.
ActivityPart1 Van de Graaff generator
If you rub socks across carpet in the right weather, you build up a static charge. Then when you
touch something, you might get a static shock. That electric shock is what we want to investigate
today. But it’s hard to build up a static charge by hand, especially in this weather.
Let’s let a machine do the work for us. The Van de Graaff generator is a simple device (look
inside!) that rubs a rubber belt across an acrylic roller. This builds up a static charge.
Observe soda can, balloon, volunteers, grounded sphere.
Notes:
1. Define conductor and insulator.
2. Explain grounding.
ElectrostaticInquiryActivity
March14–17,2017
Name:
Because the belt rubs continuously and quickly, it can generate a lot of voltage (100,000 volts
(V). Voltage measures electric potential. Potential is the potential energy at a location,
accounting for the factors that influence that form of potential energy.
Remember that there are lots of different types of potential energy we have discussed (including
gravitational, elastic, and now electric). To understand how potential is different than potential
energy, let’s first look at gravitational potential. For each of the 4 rocks shown, you know how to
calculate and explain the potential energy.
3. It is not correct to say that locations at a greater height (shown by the blue line) have
greater gravitational potential energy. Explain why not.
1kg,2m
PE=1kg*10N/m*2m
=20Nm=20J
1kg,1m,10JPE
So if we want to talk about a
value that is true of locations,
we have to account for the
mass. gravitational potential
= PE(grav) / mass.
4. Calculate the potential at
each dotted line.
3kg,2m
60J
3kg1m30JPE
When dealing with electrical energy, the electric potential is calculated by:
Electric potential = PE(elec)/charge.
The units we use for electric potential are volts (V). The symbol for electric potential in this case
is exactly the same as the unit, V, so you need to be careful to be think about whether V means the
unit (like meters) or the quantity (like distance) every time you see it.
5. . Would dropping a feather from an area with high gravitational potential be as dangerous
as dropping a bowling ball? Explain.
6. Our Van de Graaff generator can create up to 100,000V, but very little electric charge. The
third rail on Bart trains generates 1,000 V and a LOT of charge. Why is it safe to touch the
Van de Graaff but not safe to touch the rail with lower potential? Draw analogies to the
question above.
ElectrostaticInquiryActivity
March14–17,2017
Name:
Look at the diagrams below. You can read more at http://www.physicsclassroom.com/class/estatics
7. Whatisthedifferencebetweeninductionandconduction?
ElectrostaticInquiryActivity
March14–17,2017
Name:
ActivityPart2
1. Matteriseverythingthathas________and
takesup__________________.
2. Matterismadeofbuildingblockscalled
_________,andthesearemadeofsmaller
particles.Labeltheminthefollowingmodel:
3. The__________________(subatomicparticle)can
transfer,forexamplewhenmatterrubsagainsteach
other.
Followteacherdemonstration:ElectroscopeActivity
4a)Thefirst2piecesoftapehave_______________________
charge.
b)Myevidenceis(includewordsandsketch):
5a)Thenext2piecesoftapehave
________________________charge.
b)Myevidenceis(includewordsandsketch):
Triboelectricchargeischargethatisacquiredbasedonfriction(theprefixtribomeansrelated
torubbing).Somematerialsaremorelikelytogainelectrons,andothersaremorelikelytolose
them.Thetriboelectricseriesisarelativelistwheresomethingthatishighertendstogive
electronstosomethingthatislower.COMMONMISCONNCEPTION:Therelativepositionof2
itemsmaters,butstudentsoftenconfusetheoverallpositiononthelist.Forexample,glasswill
giveelectronstohumanhair,makingthehairnegativelycharged,despiteitspositionnearthe
wordpositive.
ElectrostaticInquiryActivity
March14–17,2017
Name:
6.Whenwechargedtherubberballoonbyrubbingonhumanhair,sketchthemovementofthe
electrons.Thenshowthechargeeachobjecthasafterrubbing.
Neutralobjectdemonstration
Observations
7.Providereasoningthatexplainshowattractionwascreatedbetweenthechargedballoon
andtheelectricallyneutralwall.
“MagicWands”
Weknowthataforceisdefinedasapushorapull.Aswesawwiththeelectroscope,like
chargesrepel(pushapart)andoppositechargesattract(pulltogether).
8.Useelectrostaticforces(NOTmechanicalforces-notouching,blowing,etc)toPUSHthe
suspendedtubeinacircle.Explainyourprocedureandreasoning.
ElectrostaticInquiryActivity
March14–17,2017
Name:
9.Useelectrostaticforces(NOTmechanicalforces-notouching,blowing,etc)toPULLthe
suspendedtubeinacircle.Explainyourprocedureandreasoning.
ElectrostaticInquiryActivity
March14–17,2017
Name:
ActivityPartIII
1.RobertMillikendesignedanexperimentiswhichmadeidenticaloildropletsinachamber
andwatchedthem.Whatforceactsonthedropletscausingthemtofalldown?
b)Thenozzlewasdesignedofamaterialthatishigheronthetriboelectricseriesthanoil.Asthe
oilrubbedagainstthenozzle,wereelectronsaddedorremovedfromoildrops?
(Note:Millikenusedothermethodsinadditiontothenozzle,tochargetheoildrops,soiflook
uptheexperiment,youmightfinddifferentdescriptions).
c)Anegativechargewasappliedtotheplateatthebottomofthechamber.Wouldthe
electrostaticforcepushtheoildropletsupordown?
Byvaryingthechargeontheplate,Millikencouldchangetheforcesinvolved.Hecouldexactly
balancetheforcesandmakesuspendthedropssothattheyhoveredinplace.Thenhecould
calculatetheexactchargeontheoildroplet.Bydoingthishundredsandhundredsoftimes,he
wasabletoseethatthedifferentoildropletshaddifferentnumbersofelectronsstucktothem,
buttheywerealways0.0000000000000000001602Capart.CstandsforColoumb,theunitused
tomeasurecharge.Hedeterminedthatthisnumberischargeofoneelectron,thefundamental
unitofcharge.
i.
Writethisnumberinscientificnotation.
ii.
Ifyouhave12electrons,whatwouldthechargebeinC?
ElectrostaticInquiryActivity
March14–17,2017
iii.
Name:
ConvertyouranswertonCusingthechartbelow.Asalways,showyourworkusing
correctmathematicalnotation.
-3
1 mC
milli
1 / 1,000th of a Coulomb
0.001 C
1x10 C
1 µC
micro
1 / 1,000,000th of a Coulomb
0.000001 C
1x10 C
1 nC
nano
1 / 1,000,000,000th of a Coulomb
0.000000001 C
1x10 C
iv.
-6
-9
Astaticelectricshockcanbeabout3mCtotal.Howmanyelectronsareinvolvedto
createthismuchcharge?
ElectrostaticInquiryActivity
March14–17,2017
Name:
Practice problems
1. You have access to a nylon scarf and a rubber balloon. Both are initially uncharged.
a. After rubbing them together, which of the following describes their charge states? Circle all that
apply. Feel free to consult the triboelectric series.
the scarf has become positively charged
the scarf has become negatively charged
the scarf now has more electrons in it than it did before rubbing
the balloon now has more electrons in it than it did before rubbing
the scarf now has more protons in it than electrons
the balloon now has more protons in it than electrons
the scarf now has more protons than it did before rubbing
the balloon now has more protons than it did before rubbing
b.
Upon rubbing these together, both become electrically charged. Let’s say 15.0 µC of electric
charge transferred from one to the other. How many individual electrons transferred over? Use scientific
notation.
2. You are building your own tribolectric sequence for two materials you have discovered: Vaxium and
Durapiggle. Here is the procedure from your lab notebook.
I. First, you rub a rabbit fur with a balloon. You have decided from earlier experimentation and
reading that during this process, electrons are jumping from the rabbit fur to the balloon.
II. You rub a cloth made from Vaxium on a transparent rod made from Durapiggle. After doing
this, the rod is repelled from your charged balloon.
III. You rub a bath toy made from Durapiggle on a rubber balloon. After doing this, the bath toy is
positively charged and the balloon is negatively charged.
IV. Whenever you rub rabbit fur on any of the items listed above, the rabbit fur becomes
positively charged.
Do you have enough information to write a four-item triboelectric sequence? If so, do so! If not,
explain what further steps you’d need to take with your experiment.
ElectrostaticInquiryActivity
March14–17,2017
Name:
3. Two uncharged metal spheres are attached to insulating supports. They are brought into contact with
one another. You generate a positive static charge on an insulating rod and bring it nearby, as shown.
You do not touch the rod to the spheres.
a. You then pull the rod away, and then physically separate the two spheres by pulling the bases
apart. What is the charge state of each of the spheres afterward?
b. This time, you separate the spheres while the rod is still nearby to sphere 1. Then you remove the
rod. What is the charge state of each of the spheres as a result?
4. The diagram at right shows the process of charging by induction. In the space below, explain in words
what is happening.