SP212 Lab: One  Electrostatics
Version: January 14, 2015
PHYSICS II
LAB 1
SP212
ElectrostaticsPre‐LabAssignment
1. Anelectroscopeconsistsofneutral(uncharged)conductingmaterialincontactwith
twogoldleavesatthebottom(whicharealsoconducting).Apositivelycharged
conductingrodisbroughtcloseto,butisnotallowedtotouchtheelectroscope.
Whatisthesignofthenetchargeoneachofthegoldleaves?
A.Oneisnegative,oneispositive.
B.Botharenegative.
C.Botharepositive.
D.Zerobecausethenetchargeinaconductoris0.
E.Zerobecausethereisnocontactwiththeconductingrod.
Explain:
2. Instead,anegativelychargedrubberrodisbroughtneartheknobofapositively
chargedelectroscope.Theresultisthat:
A.theelectroscopeleaveswillmovefartherapart.
B.therodwillloseitscharge.
C.theelectroscopeleaveswilltendtocollapse.
D.theelectroscopewillbecomedischarged.
E.nothingnoticeablewillhappen.
Explain:
Page 1 of 2 SP212 Lab: One  Electrostatics
Version: January 14, 2015
3. Each of the spheres (balls) in the below diagram are made of pith (a light weight
spongelikematerialfoundinsomeplants)andstartthescenarioneutrallycharged.
The pith balls, of mass m, are then charged, by touching them with a charged rod,
suchthatthenoweachballhasthesameamountofchargelittleq.Assumetheballs
arenotacceleratingandthatthetaisasmallangle.
a) Draw the Free Body Diagram for the forces acting on the ball attached to the string of length L.
b) Write the Newton’s second law expression for the sum of the forces in the x‐direction. c) Write the Newton’s second law expression for the sum of the forces in the y‐direction. d) Student X claims that the formula for the electrostatic force of this pendulum device is approximately FE 
m g X ball
. L
Is that student correct? Why or why not? ShowAllWork:
Page 2 of 2