Physics Investigatory Project
Manjunath Naik
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Physics Investigatory Project
Manjunath Naik
INVESTIGATORY PROJECT ON:-
TO ESTIMATE THE CHARGE INDUCED ON EACH OF THE TWO IDENTICAL STRYO FOAM (OR PITH) BALLS SUSPENDED IN A VERTICAL PLANE BY MAKING USE OF COULOMBS LAW.
By:-
Manjunath Naik Class: 12th Section A Roll no.
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Physics Investigatory Project
Manjunath Naik
INDEX TOPICS
Page no.
1.
CERTIFICATE
4
2.
ACKNOWLEDGEMENT
5
3.
OBJECTIVE
6
4.
INTRODUCTION
7
5.
MATERIALS AND EQUIPMENT
8
6.
THEORY
9
7.
PROCEDURE
13
8.
OBSERVATION
14
9.
CONCLUSION AND RESULT
15
10. PRECAUTIONS
16
11. SOURCES OF ERROR
16
12. BIBLIOGRAPHY
17
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Physics Investigatory Project
Manjunath Naik
CERTIFICATE Ryan International School
This is hereby to certify that the Project titled “TO ESTIMATE THE CHARGE INDUCED ON EACH OF THE TWO IDENTICAL STRYO FOAM (OR PITH) BALLS SUSPENDED IN A VERTICAL PLANE BY MAKING USE OF COULOMBS LAW” was successfully completed by Manjunath Naik, student of class XII Ryan Sanpada under the guidance of Mr Amit Kumar during the academic year 2017-2018.
External’s Signature:
Internal’s Signature:
Principal’s Signature:
School Stamp
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Physics Investigatory Project
Manjunath Naik
ACKNOWLEDGEMENT I wish to express my deep gratitude and sincere thanks to the Principle, Mrs Murial Fernandez, Ryan International School, Sanpada for her encouragement and for all the facilities she has provided for this project work. I extend my hearty thanks to my subject teacher Mr Amit Kumar and Lab Assistant Devesh Sir who guided me to the successful completion of this project. I take this opportunity to express my deep sense of gratitude for their invaluable guidance, constant encouragement and immense motivation which has sustained my efforts at all stages of this project work. I can’t forget to offer my sincere thanks to my classmates who helped me to carry out this project work successfully and for their valuable advice and support which I received for them time to time.
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Physics Investigatory Project
Manjunath Naik
Objective To estimate the charge induced on each one of the two identical styro foam balls (or pith balls) suspended in a vertical plane by making use of
Coulomb’s law:-
1 2 || = ke
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Physics Investigatory Project
Manjunath Naik
INTRODUCTION When it is only of interest to know the magnitude of the electrostatic force (and not its 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 force F acting simultaneously on two point charges q1 and q2 as follows:
1 2 || = ke
where r is the separation distance and k e is Coulomb’s constant. If the product q 1q2 is positive, the force between the two charges is repulsive; if the product is negative, the force between them is attractive.
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Physics Investigatory Project
Manjunath Naik
Material and Equipment
Small size identical balls (pitch or soft plastic)
Physical balance or electrical balance
Half meter scale
Cotton thread
Small stand
Glass rod
Silk cloth
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Physics Investigatory Project
Manjunath Naik
THEORY The fundamental concept in electrostatics is electrical charge. We are all familiar with the 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:
=k
1
e
2
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).
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Physics Investigatory Project
Manjunath Naik
The study of the Coulomb forces among arrangements of stationary charged particles is called electrostatics. Coulomb’s Law describes three properties of the electrical
force: 1)The force is inversely proportional t o t h e s q u a r e o f t h e distance between the charges, and is directed along the straight line that connects their centres. 2)The force is proportional to the p r o d u c t o f t h e m a g n i t u d e o f the charges. 3)Two the
particles same
of
charge
exert
a
repulsive
force
on
each other, and
two particles 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 negatively charged 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 10
Physics Investigatory Project
Manjunath Naik
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 carry an electrical current. Other materials such as glass are insulators. Their electrons are bound 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 11
Physics Investigatory Project
Manjunath Naik
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 an isolated, 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 over to 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.
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Physics Investigatory Project
Manjunath Naik
PROCEDURE 1. Measure the mass (m) of each of the two identical pith balls using a physical balance. 2. Hang the two balls from a rigid support using light silk or cotton threads of same length ‘l’.
3. Rub the glass tod silk cloth to induce charge on it. Now touch the glass rod with both the pith balls together so that equal charge is induced on both the balls. 4. When left freely, the two balls will repel each other. Measure the distance between the balls when are at rest. Note down the distance. 5. To change the charge on ball, take third uncharged ball touch it to any one of the two balls and take the third ball away, and repeat step 4. 6. Take other uncharged suspended with other uncharged 4th ball and take the 4th ball away and repeat step 4.
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Physics Investigatory Project
Manjunath Naik
OBSERVATIONS
Mass of the pith balls m = 200 gm.
Radius of the ball a = 0.2 cm.
Length of thread l = 100 cm.
Sl.no.
Charge on Ball B1
Charge on Ball B2
1 2 3 4
0.00µC 2.00µC 2.00µC 1.00µC
0.00µC 2.00µC 1.00µC 1.00µC
Distance between the two balls (in cm) 0.4cm 33.0cm 26.2cm 20.8cm
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Physics Investigatory Project
Manjunath Naik
Calculation and Result Let the force between two stationary charges be F.
= k 1
2
e
The weight of the ball w = mg The restoring force on each ball = mg sinθ From the diagram in the right in triangle ABC
Sinθ =
Let the charge on each ball be q 1, q2 and q3 then at equilibrium
q×q mg sinθ =
3 Charge on the pith ball = √
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Physics Investigatory Project
Manjunath Naik
Precautions 1.) The suspended balls should not be touched by any conducting body. 2.) Rub the glass rod properly with silk rod to produce more charge. 3.) Weight the mass of the balls accurately.
SOURCES OF ERROR
The balls may not be of equal size and mass.
The distance between the balls may be measured inaccurately.
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Physics Investigatory Project
Manjunath Naik
BIBLIOGRAPHY
iCBSE.com
Wikipedia
Chemmicalland.com
Books.google.co.in
Physics NCERT class 12 book
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