Investigatory Project Physics

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12  CBSE INVESTIGATORY PROJECT. RMK RESIDENTIAL SENIOR SECONDARY SCHOOL

S.K.RUPIKA   

Xll-‘B

CERTI!ICATE  

This is to certify that the PHYSICS project titled “Electromagnetic Induction” has been successfully completed by S!"upi#a of class $ll%&'()"*! "esidential Senior Secondary School) in the partial fulfillment by Central 'oard +f Secondary Education ,C'SE- leading to the a.ard of the annual e/amination of the year 0123 %0124

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 ACKNO"LEDGEMENT  

“ There are times when silence speak so much more louder than words of praise to only as good as belittle a person, whosewords do not express, but only put a veneer over true feelings, which are of gratitude at this point of time.” 

I .ould li#e to e/press my sincere gratitude to my physics mentor *" *urali !rishna) for his 8ital support) guidance and encouragement) .ithout .hich this project .ould not ha8e come forth I .ould also li#e to e/press my gratitude to the +THE" staff of the 9epartment of Physics for their support during the ma#ing of this project

TO ESTIMATE THE   CHARGE INDUCED ON  EACH O! THE T"O  IDENTICAL STRYO !OAM  #OR PITH$ BALLS  SUSPENDED IN A  VERTICAL PLANE BY   MAKING USE O!   COULOMBS LA"  

Coulomb Coulomb graduated in 5o8ember 2:;2 from i?res +8er the ne/t t.enty years he .as posted to a 8ariety of locations .here he .as in8ol8ed in engineering % structural) fortifications) soil mechanics) as .ell as other fields of engineering His first posting .as to 'rest but in @ebruary 2:;3 he .as sent to *artiniAue) in the Best Indies) .here he .as put in charge of building the ne. @ort 'ourbon and this tas# occupied him until une 2::0 +n his return to @rance) Coulomb .as sent to 'ouchain Ho.e8er) he no. began to .rite important .or#s on applied mechanics and he presented his first .or# to the 6cad=mie des Sciences in Paris in 2::D In 2:: Coulomb .as sent to "ochefort to collaborate .ith the *arAuis de *ontalembert in constructing a fort made entirely from .ood near Ile dF6i/ 9uring his period at "ochefort) Coulomb carried on his research into mechanics) in particular using the shipyards in "ochefort as laboratories for his e/periments Gpon his return to @rance) .ith the ran# of Captain) he .as employed at 7a "ochelle) the Isle of 6i/ and Cherbourg He disco8ered an in8erse relationship of the force bet.eenelectric charges and the sAuare of its distance) later named after him as CoulombFs la.

C+G7+*'(S 76B In 2:4 6ugustine de Coulomb in8estigated the attracti8e and repulsi8e forces bet.een charged objects) e/perimentally formulating .hat is no. referred to as Coulomb(s 7a. “The magnitude of the electric force that a particle e/erts on another is directly proportional to the product of their charges and in8ersely proportional to the sAuare of the distance bet.een them” *athematically) this electrostatic @ acting on t.o charged particles ,A2) A0- is e/pressed as

.here r is the separation distance bet.een the objects and # is a constant of proportionality) called the Coulomb constant) k = 9.0 × 109 N · m2/C2. This formula gi8es us the magnitude of the force as .ell as direction by noting a positi8e force as attracti8e and a negati8e force as repulsi8e 5oting that li#e charges repel each other and opposite charges attracting each other) Coulomb measured the force bet.een the objects) small metal coated balls) by using a torsion balance similar to the balance used to measure gra8itational forces

+'ECTIJE% To estimate the charge induced on each of the t.o identical styro foam ,or pith- balls suspended in a 8ertical plane by ma#ing use of coulomb(s la.

*6TE"I67S "EKGI"E9% Small si>e identical balls ,pitch or soft plastic Physical balance or electronic balance  Halfmeter Scale  Cotton thread  Stand  Llass rod ,or plastic rod Sil# cloth ,or .ollen cloth

THE+"Y% The fundamental concept in electrostatics is electrical charge Be are all familiar .ith the fact that rubbing t.o materials together M for e/ample) a rubber comb on cat fur M produces a “static” charge This process is called charging by friction Surprisingly) the e/act physics of the process of charging by friction is poorly understood Ho.e8er) it is #no.n that the ma#ing and brea#ing of contact bet.een the t.o materials transfers the charge The charged particles .hich ma#e up the uni8erse come in three #inds positi8e) negati8e) and neutral 5eutral particles do not interact .ith electrical forces Charged particles e/ert electrical and magnetic forces on one another) but if the charges are stationary) the mutual force is 8ery simple in form and is gi8en by CoulombFs 7a.

.here @ is the electrical force bet.een any t.o stationary charged particles .ith charges A2 and A0,measured in coulombs-) r is the separation bet.een the charges ,measured in meters-) and # is a constant of nature ,eAual to N21  5m0OC0 in SI units- The study of the Coulomb forces among arrangements of stationary charged particles is called electrostatics CoulombFs 7a. describes three properties of the electrical force

2

The force is in8ersely proportional to the sAuare of the distance bet.een the charges) and is directed along the straight line that connects their centers

0

The force is proportional to the product of the magnitude of the charges

D

T.o particles of the same charge e/ert a repulsi8e force on each other) and t.o particles of opposite charge e/ert an attracti8e force on each other

*ost of the common objects .e deal .ith in the macroscopic ,human%si>ed- .orld are electrically neutral They are composed of atoms that consist of negati8ely charged electrons mo8ing in Auantum motion around a positi8ely charged nucleus The total negati8e charge of the electrons is normally e/actly eAual to the total positi8e charge of the nuclei) so the atoms ,and therefore the entire object- ha8e no net electrical charge Bhen .e charge a material by friction) .e are transferring some of the electrons from one material to another

*aterials such as metals are conductors Each metal atom contributes one or t.o electrons that can mo8e relati8ely freely through the material 6 conductor .ill carry an electrical current +ther materials such as glass are insulators Their electrons are bound tightly and cannot mo8e Charge stic#s on an insulator) but does not mo8e freely through it

 6 neutral particle is not affected by electrical forces 5e8ertheless) a charged object .ill attract a neutral macroscopic object by the process of electrical polari>ation @or e/ample) if a negati8ely charged rod is brought close to an isolated) neutral insulator) the electrons in the atoms of the insulator .ill be pushed slightly a.ay from the negati8e rod) and the positi8e nuclei .ill be attracted slightly to.ard the negati8e rod Be say that the rod has induced polari>ation in the insulator) but its net charge is still >ero

The polari>ation of charge in the insulator is small) but no. it(s positi8e charge is a bit closer to the negati8e rod) and its negati8e charge is a bit farther a.ay Thus) the positi8e charge is attracted to the rod more strongly than the negati8e charge is repelled) and there is an o8erall net attraction If the negati8e rod is brought near an isolated) neutral conductor) the conductor .ill also be polari>ed In the conductor) electrons are free to mo8e through the material) and some of them are repelled o8er to the opposite surface of the conductor) lea8ing the surface near the negati8e rod .ith a net positi8e charge The conductor has been polari>ed) and .ill no. be attracted to the charged rod 5o. if .e connect a conducting .ire or any other conducting material from the polari>ed conductor to the ground) .e pro8ide a “path” through .hich the electrons can mo8e Electrons .ill actually mo8e along this path to the ground If the .ire or path is subseAuently disconnected) the conductor as a .hole is left .ith a net positi8e charge The conductor has been charged .ithout actually being touched .ith the charged rod) and its charge is opposite that of the rod This procedure is called charging by induction

7et the force bet.een t.o stationary charges be @

The Beight of the ball  

Bmg

The restoring force on each ball sin θ

mg

@rom the diagram in the right In triangle 6C' sin θ

 x 2l



7et the charge on each ball is  

A2A0A

Then at eAulilibrium mg

sin θ

mg

 x 2l

 

kq×q  x kq  x

2

2

2

3

 g

mgx 2 lk 

P"+CE9G"E%

2- Beight the mass of each identical pitch balls by balance and note do.n it 0- Tie the balls .ith t.o sil# or cotton threads and suspend at a point on a stand or a rigid support *easure the length of threads by half meter scale The length of threads should be eAual 5ote do.n the length D- "ub the glass rod .ith sil# cloth and touch .ith both balls together so that the balls acAuired eAual charge 3- Suspend the balls freely and the balls stay a.ay a certain distance bet.een the balls .hen they become stationary 5ote do.n the distance 4- Touch any one suspended ball .ith other uncharged third ball and ta#es the third ball a.ay and repeat the step 3 ;- Touch other suspended ball .ith other uncharged fourth ball and ta#es the fourth ball a.ay and repeat the step 3

+'SE"J6TI+5% 2 *ass of each ball),m QQQQQg 0 "adius of each ball),r-  QQQQQmm D 7ength of each thread),l-  QQQQQcm

S.NO

CHARGE ON BALL A q ( 1 )

1.

2.

.

!.

Calculations% 'y using the relation

CHARGE ON BALL B q ( 2 )

DISTANCE BETWEEN THE BALLS (x cm)

3

 g

mgx 2 lk 

Calculate the charge in each case

"ESG7TS% The charge on each ball  QQQQQQQC

P"EC6GTI+5S% 2 The suspended balls should not be touched by any conducting body 0 "ub the glass rod properly .ith the sil# cloth to produce more charge D Beight the mass of the balls accurately

S+G"CE +@ E""+"% 2 The balls may not be of eAual si>e and mass 2. The distance bet.een the balls may be measured accurately