NARAYANA OLYMPIAD SCHOOL
MOGAPPAIR, CHENNAI – 600037
AISSCE 2024-25
Roll No:
Name :
Title : “To estimate the charge induced on each one of the two identical Styrofoam balls (or pith
balls) suspended in a vertical plane by making use of Coulomb’s law”.
PHYSICS PROJECT
DEPARTMENT OF PHYSICS
2024-2025
NARAYANA OLYMPIAD SCHOOL
CERTIFICATE
This is to certify that the project work titled “To estimate the charge induced on each one of the
two identical Styrofoam balls (or pith balls) suspended in a vertical plane by making use of
Coulomb’s law” is the bonafide record of project work done by Master/ Miss
_____________________of Grade XII during the academic year 2024-2025, under my supervision
and guidance.
Submitted for AISSCE -2025 Physics Practical Examination held on at Narayana Olympiad School,
Chennai.
Teacher in charge
PRINCIPAL INTERNAL EXAMINER EXTERNAL EXAMINER
DECLARATION
I hereby declare that the project work entitled “To estimate the charge induced on each one of the
two identical Styrofoam balls (or pith balls) suspended in a vertical plane by making use of
Coulomb’s law” submitted to Department of Physics, Narayana Olympiad School, is prepared by
me.
Signature of the student
ACKNOWLEDGEMENT
First of all, I thank our beloved parents for providing us the opportunity to study in Narayana
Olympiad School, Mogappair.
I would like to thank our beloved Director, Dr. P. Narayana for being our motivational force
for the completion of this project.
I thank our beloved Dean, Sri. Gaddipati Satyanarayana for supporting in all the ways to
complete the project.
I thank our Principal, Sri. Krishna Kishore for his exceptional support.
I would like to extend my deepest gratitude to our faculties of Physics Department, Mr. Deepak
Kumar Gupta, Mr. Jay S Sawant, Mr. Sandeep, Mr. Aravind, Dr. Venkateswara Reddy,
Mr. Mohammad Daniyal Khan, Mrs. Amrutha, Mrs. Poonguzhali, and Mr. Sudhakar for
encouraging, helping and guiding me to complete this project.
I would like to acknowledge and express my gratitude to Mr. Vinoth Kumar for his assistance
in creating the preliminary pages of the project. His contributions were invaluable and greatly
appreciated.
Last but not the least I thank all my friends who helped me in the completion of this project.
Table of Contents
1 OBJECTIVE: .............................................................................................................. 6
2 ABSTRACT ................................................................................................................ 6
3 THEORY .................................................................................................................... 6
4 MATERIALS REQUIRED: ........................................................................................ 9
5 PROCEDURE: ............................................................................................................ 9
6 OBSERVATIONS: ................................................................................................... 10
7 RESULT: .................................................................................................................. 10
8 REFERENCES.......................................................................................................... 11
1 OBJECTIVE:
To estimate the charge induced on each one of the two identical Styrofoam balls (or pith balls)
suspended in a vertical plane by making use of Coulomb’s law
2 ABSTRACT
When it is only of interest to know the magnitude of the electrostatic force (and notits direction),
it may be easiest to consider a scalar version of the law. The scalar form of the Coulomb’s Law
relates the magnitude and sign of the electrostatic forceF acting simultaneously on two point
charges q1 and q2 as follows:
where r is the separation distance
ke is Coulomb’s constant.
If the product q1q2 is positive, the force between the two charges is repulsiveif the product is
negative, the force between them is attractive.
3 THEORY
The fundamental concept in electrostatics is electrical charge. We are all familiar withthe fact that
rubbing two materials together - for example, a rubber comb on cat fur- produces a “static”
charge. This process is called charging by friction.
The charged particles which make up the universe come in three kinds: positive,negative,
and neutral. Neutral particles do not interact with electrical forces. Charged particles exert
electrical and magnetic forces on one another, but if the charges are stationary, the mutual force
is very simple in form and is given by Coulomb’s Law:
Where, F is the electrical force between any two stationary charged particles with charges q1
and q2(measured in coulombs), r is the separation between the charges (measured in meters),
and k is a constant of nature (equal to 9x109 Nm2/C2 in SI units).
The study of the Coulomb forces among arrangements of stationary charged particlesis called
electrostatics. Coulomb’s Law describes three properties of the electrical force:
• The force is inversely proportional to the square of the distance between the charges,
and is directed along the straight line that connects their centres.
• The force is proportional to the product of the magnitude of the charges.
• Two particles of the same charge exert a repulsive force on each other, and twoparticles
of opposite charge exert an attractive force on each other.
Most of the common objects we deal with in the macroscopic (human-sized) world are
electrically neutral. They are composed of atoms that consist of negativelycharged electrons
moving in quantum motion around a positively charged nucleus. The total negative charge of
the electrons is normally exactly equal to the total positive charge of the nuclei, so the atoms
(and therefore the entire object) have no net electrical charge. When we charge a material by
friction, we are transferring some of the electrons from one material to another.
Materials such as metals are conductors. Each metal atom contributes one or two electrons that
can move relatively freely through the material. A conductor will carryan electrical current.
Other materials such as glass are insulators. Their electrons arebound tightly and cannot move.
Charge sticks on an insulator, but does not move freely through it.
A neutral particle is not affected by electrical forces. Nevertheless, a charged object will attract
a neutral macroscopic object by the process of electrical polarisation. For example, if a
negatively charged rod is brought close to an isolated, neutral insulator,the electrons in the atoms
of the insulator will be pushed slightly away from the negative rod, and the positive nuclei will
be attracted slightly toward the negative rod. We say that the rod has induced polarisation in the
insulator, but its net charge is still zero.
The polarisation of charge in the insulator is small, but now it’s positive charge is a bit closer to
the negative rod, and its negative charge is a bit farther away. Thus, the positive charge is
attracted to the rod more strongly than the negative charge is repelled, and there is an overall
net attraction. If the negative rod is brought near anisolated, neutral conductor, the conductor
will also be polarised. In the conductor, electrons are free to move through the material, and
some of them are repelled overto the opposite surface of the conductor, leaving the surface near
the negative rod with a net positive charge. The conductor has been polarised, and will now be
attracted to the charged rod. Now if we connect a conducting wire or any other conducting
material from the polarised conductor to the ground, we provide a “path” through which the
electrons can move. Electrons will actually move along this path to the ground. If the wire or
path is subsequently disconnected, the conductor as a whole is left with a net positive charge.
The conductor has been charged without actually being touched with the charged rod, and its
charge is opposite that of the rod. This procedure is called charging by induction.
4 MATERIALS REQUIRED:
• Small size identical balls (pitch or soft plastic)
• Physical balance or electrical balance
• Half meter scale
• Cotton thread
• Small stand
• Glass rod
• Silk cloth
5 PROCEDURE:
• Measure the mass (m) of each of the two identical pith balls using a physicalbalance.
• Hang the two balls from a rigid support using light silk or cotton threads of samelength ‘l’.
• Rub the glass tod silk cloth to induce charge on it. Now touch the glass rod withboth the pith
balls together so that equal charge is induced on both the balls.
• When left freely, the two balls will repel each other. Measure the distance betweenthe balls when
are at rest. Note down the distance.
• To change the charge on ball, take third uncharged ball touch it to any one of thetwo balls and
take the third ball away, and repeat step 4.
• Take other uncharged suspended with other uncharged 4th ball and take the 4thball away and
repeat step 4.
6 OBSERVATIONS:
Mass of the pith balls m= 200 gm.
Radius of the ball a = 0.2 cm.
Length of thread l = 100 cm.
7 RESULT:
Let the force between two stationary charges be F
• The weight of the ball w = mg
• The restoring force on each ball = mg sinθ. From the diagram in the right in triangle
ABCSinθ = x/2l
• Let the charge on each ball be q1, q2 and q3 then at equilibriummg sinθ = (kq×q)/x2
• Charge on the pith ball =√((mgr3)/2kl)
8 REFERENCES
• iCBSE.com
• Wikipedia
• Chemmicalland.com
• Books.google.co.in
