7/21/2019 Sample Prelab

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Name:Date:Course and section :

Pre lab 1:Electrostatic Force

Purpose

Purpose of this experiment is to nd the unknown value of a! in thesimplied Coulomb!s law which states that the force "F# between twobodies of e$ual char%e "$# separated b& a distance r is F ' C1r

a( whereC1is a constant and is e$ual to k$

)where k is the Coulomb!s constant*

+nderl&in% principle

,n this experiment( the repulsive force is proportional to the tor$ue on

the torsion wire( which in turn is proportional to the restorin% an%le *

-his allows us to write the simplied Coulomb!s law as ' C)rawhere

C)is a new constant which is a function of C1and depends on theapparatus* -akin% the natural lo% on both sides( the new e$uation can

be written as ln"# ' a.ln"r# / ln"C)#* -his relationship shows that the

slope of a ln"# vs* ln"r# plot should %ive us the value of a!*

0ethod

torsion balance will be used in this experiment* -wo %raphite coatedpin% pon% balls will be kept at a certain distance apart "r# and will bechar%ed* -he han%in% ball will swin% awa& and will twist the torsion

wire* -he dial on top of the apparatus will be turned b& to restore

the ali%nment* 0ultiple values of r and will be determined* Finall&(

we will plot ln"# vs* ln"r# to determine the value of a from the slope*