Best project for class 12

1. Scindia Kanya Vidyalaya
Session:-2020-21
Submitted to: - Submitted by:-
Mrs. Reita Singh Vidhi Bhutia

2. Contents
1) Certificate
2) Acknowledgement
3) Introduction
4) Positive and Negative Electricity
5) Insulators and Conductors
6) The Gold-Leaf Electroscope
7) Experiments with a Gold Leaf Electroscope
8) Electrostatic Induction
9) The Electron Theory Atomic Structure
10) Electrification by Friction
11) Electrons in Insulators and Conductors
12) Distribution of Charge over the Surface of a
Conductor
13) No Charge on the Inside Surface of a Hollow
Charged Conductor
14) Some Uses of Frictional Electricity
15) Bibliography

3. Scindia Kanya Vidyalaya
This is to certify that Vidhi Bhutia, a student of class
XII ‘A’ has successfully completed the project titled
“Frictional Electricity” under the guidance of
Reita Singh (Subject teacher), during the academic year
2020-21in partial fulfilment of Physics practical
examination conducted by______________.
___________ ___________
(Signature of (Signature of
External examiner) Physics teacher)

4. In the accomplishment of this project successfully,
many people have best owned me their blessings and
the heart pledged support, this time I am utilizing to
thank all the people who have been concerned with
project.
Primarily, I would thank god for being able to complete
this project with success. Then I would like to thank my
principal Mrs. Nishi Misra and Physics teacher
Mrs.Reita Singh whose valuable guidance has been the
ones that helped me patch this project and make it full
proof success. Her suggestions and her instructions
have served as the major contributor towards the
completion of this project.
Then I would like to thank my parents and friends who
have helped me with their valuable suggestions and
their guidance has been helpful in various phrases of the
completion of the project.

5. Introduction
Everyone is familiar with the fact that if a pen made of certain plastic
materials is rubbed on the coat-sleeve it will afterwards attract dust
and small pieces of paper. The same, effect if noticed when a mirror
or window-pane is polished with a dry cloth in a very dry atmosphere.
Dust and fluff from the cloth stick to the glass and are difficult to
remove. Perspex, cellulose acetate and the vinyl compounds used for
gramophone records also show the attraction, but to a more marked
degree. The phenomenon is called electric attraction, and the rubbed
materials are said to have become charged with frictional electricity.
Knowledge of it goes back as far as the sixth century B.C., when the
Greek Philosopher, Thales, described the attractive properties of
rubbed amber. The word electricity has, in fact, been derived from the
Greek word "elektron", meaning amber.
Friction between certain textiles can also produce electrification.
Robert Symmer first described this in the early eighteenth century.
Electrification by friction is sometimes associated with a crackling
sound. This may be heard when very dry hair is combed with a
vulcanite comb, or when an ebonite or alkathene rod is vigorously
rubbed with fur. The cracking is caused by small electric sparks,
which may be seen if the room is in darkness. Sparks from frictional
electricity can be very dangerous when inflammable vapour is
present. Nowadays, accidents are prevented by allowing a short length
of chain to trail from the metal frame of the trolley. This conducts the
electric charge away to earth, where it can do no harm.

6. Positive and Negative Electricity
Electric repulsion was first described in 1672 by Otto von Guericke,
who noticed that some feathers were attracted to a charged sulphur
ball and then repelled from it. One hundred and fifty years later in
France, Charles Du Fay discovered that charged bodies did not always
repel each other, but that sometimes attraction took place. He came to
the conclusion that there were two kinds of electricity. Charges of the
same kind repel, while charges of opposite kinds attract one another.
To distinguish between the two kinds, Du Fay used the terms vitreous
and resinous electricity. Vitreous (from the Latin vitrum = glass)
electricity is obtained when glass is rubbed with silk, and resinous
electricity is obtained when amber, sealing-wax, sulphur, shellac, and
a host of other substances are rubbed with fur or flannel. Later on,
these terms were found to be misleading, since, for example, ground
glass gives resinous electricity and very highly polished ebonite gives
vitreous electricity. Accordingly, Benjamin Franklin introduced the
present day terms positive and negative instead of vitreous and
resinous respectively.
Insulators and Conductors
When current electricity was discovered, 200 years after the
publication of Gilbert’s book, it was found that an electric current
would flow through a non electric but not through an electric.
Accordingly, these terms became obsolete. We now call an electric an
insulator and a non-electric a conductor.
Gilbert mentions the importance of dryness an electrical experiments.
Impure water is a conductor, and a film of moisture from
condensation or moist hands on the surface of an insulator allows
electricity to be conducted away to earth. For successful results, all
apparatus used in electrical experiments must be thoroughly dry.
Glass rods in particular are best warmed before use.

7. The Gold-Leaf Electroscope
For the detection and testing of small electric charges, a gold-leaf
electroscope is used. This instrument was invented towards the end of
the eighteenth century by a Yorkshire clergyman named Abraham
Bennet. Fig. shows a common type of electroscope. It consists of a
brass rod surmounted by a brass disc or cap and having at its lower
end a small rectangular brass plate with a leaf of thin gold or
aluminium attached. The leaf is protected from draughts by enclosing
it in an earthed metal case with glass windows. The brass rod is
supported by passing it through a plug of some good insulating
material such as alkathene at the top of the case.
The three horizontal parallel lines shown at E in fig. is the
conventional symbol for an earth connection.

8. Experiments with a Gold Leaf Electroscope
(1) To detect the presence of charge on a body
If a rod of some suitable material is charged by friction and then
brought near to the cap of a gold leaf electroscope the leaf is seen to
diverge from the plate. A charge has been induced on the leaf and
plate, and consequently repulsion occurs between them. On removing
the charged rod, the leaf collapses, showing that the induced charge
on the electroscope is only temporary.
Very small charges may be detected by this method.
(2) To Charge a gold-leaf electroscope by contact
An ebonite rod is given a small charge by rubbing with fur, and is
then rolled over the cap of an electroscope. The leaf will be seen to
diverge, and then the rod is removed. If the leaf does not stay
diverged the process is repeated until it does. We may now assume
that the electroscope is charged with negative electricity by
conduction from the ebonite rod.
If the cap of the electroscope is touched with the finger the charge
flows to earth through the experimenter’s body and the leaf collapses.
This is called "earthing the electroscope".
(3) To test for the sign of the charge on a body
Having charged the electroscope negatively, the ebonite rod should be
recharged and brought near to the cap. An increase in the leaf
divergence is noted.
A glass road rubbed with silk (positive charge) is now cautiously
brought down towards the cap from a height of about 50 cm. This
time, a decrease in divergence is noticed.
The electroscope is discharged by touching it with the finger and
afterwards charged positively by contact, using a glass rod rubbed

9. with silk. We shall now find that an increased divergence is caused by
bringing a charged glass rod near the cap decreased divergence by a
charged ebonite rod.
From these experiments we conclude that an increase in divergence
occurs when the charge on the electroscope and the test charge
are of the same kind.
The results of these experiments are summarized in the table :
Charge on
Electroscope
Charge brought
Near cap
Effect on leaf
divergence
+ + Increase
- - Increase
+ - Decrease
- + Decrease
+ or - Uncharged body Decrease
(4) To test the insulating properties of various materials
The insulating or, conversely, the conducting property of a given
substance may be tested by holding a sample of the substance in the
hand and then bringing it into contact with the cap of a charged
electroscope. If the substance is a good insulator there will be no
leakage of charge through it and the leaf divergence will not alter. If,
however, the leaf collapses instantly it shows that the substance is a
good conductor.

10. Electrostatic Induction
We saw earlier that a charged rod brought near to the cap of an
electroscope causes the leaf to diverge from the plate, showing that a
charge has been induced on both of them. The following experiment
provides more information about the charges which are induced on an
insulated conductor when a charged rod is brought near it.
(a) Two insulated brass spheres A and B are placed together so that
they touch one another and thus form, in effect, a single conductor.
(b) A negatively charged rod is now brought near to A. As a result, a
positive charge is induced on A and a negative charge on B.
(c) Still keeping the charged rod in position, sphere B is moved a
short distance from A.
(d) The charged rod is now removed and A and B are tested for
charge.

11. The test is carried out as follows. Sphere A is brought near to the cap
of a positively charged electroscope. An increase in divergence shows
that it is positively charged. Similarly, sphere B produces an increase
in divergence when it is brought near to the cap of a negatively
charged electroscope, thus showing it to be negatively charged.
In the whole experiment is carried out again using a positively
charged rod as the inducing charge, the induced charges on A and B
are reversed.
The Electron Theory Atomic Structure
Towards the end of the nineteenth century, Sir J.J.Thomson carried
out some experiments with an electric discharge through a tube
containing air at very low pressure. Following this investigation he
came to the conclusion that negative electricity consists of tiny
particles which came to be called electrons. During the succeeding
years it became apparent that these negative electrons actually formed
part of the atoms of which all substances are composed.
Electrification by Friction
When a glass rod is rubbed with a silk cloth some electrons from the
glass attach themselves to the silk. Consequently, the glass becomes
positively charged and the silk negatively charged. Likewise when
ebonite is rubbed with fur electrons are transferred from fur to
ebonite, thus making the ebonite negative and the fur positive.

12. Electrons in Insulators and Conductors
The difference between an insulator and a conductor is that, in an
insulator, the electrons are firmly bound to their atoms and will not
move of their own accord, whereas in a conductor the electrons are
able to move freely from one atom to another.
If an ebonite rod is held in the hand and rubbed with fur a charge of
electrons is formed on its surface. These electrons cannot flow to
earth through the hand, since they are unable to move through the
insulating ebonite. When a brass rod is rubbed with fur it becomes
charged with electrons in just the same way as the ebonite. However,
the charge cannot be detected, since it is immediately conducted
through the brass and the hand to earth. This may be prevented by
mounting the brass rod on an insulating handle. The charge cannot
now be conducted away, and its presence can be detected by bringing
the rod near a gold-leaf electroscope. The charge can be tested and
found to be negative by showing that there is no increase in
divergence when the brass rod is brought near to the cap of a
negatively charged electroscope.
Distribution of Charge Over the Surface of a Conductor
A proof plane and gold-leaf electroscope may be used to investigate
the distribution of charge over the surface of a conductor, by pressing
the proof plane into contact with the surface at various places in turn
and then transferring the charge to the electroscope. The divergence
of the leaf will give a rough measure of the amount of charge
transferred, and hence some idea of the surface density of the charge.
Surface density is defined as the quantity of charge per unit area of
surface of a conductor.

13. Fig. also shows how charge is distributed over the surface of
conductors of different shapes. In these diagrams the distance of the
dotted line from the surface is proportional to the surface density at
any point. The most important fact shown by this experiment is that
charge is mostly concentrated at places where the surface is sharply
curved. This is particularly noticeable at the pointed end of the pear-
shaped conductor.
No charge on the Inside Surface of a Hollow Charged Conductor
The electric conductors used in the experiments we have described
are generally made of hollow brass or else of wood covered with
tinfoil. No advantage is to be gained by making them of solid metal,
since the charge resides only on the outside surface. The following
experiment illustrates this fact.
Charles Coulomb demonstrated that charge always resides on the
outside surface of a conductor with the aid of two hemispherical cups
which fitted exactly round an insulated metal sphere.
The sphere first charged, and afterwards the hemispheres are fitted
over it while being held by insulating handles. On removing the

14. hemispheres they are found to be charged, but no charge at all
remains on the sphere. This shows that all the charge on the sphere
must have passed to the outside of the hemispheres.
Some Uses of Frictional Electricity
1. Photocopying machines or zerox machines
Based on the attraction of powdered particles to a metal drum that
carries a pattern of charge that is same as the pattern of the desired
image.
2. Paint Droplets become charged by friction
When they are sprayed, if the object to be painted such as a car body,
is given a charge of opposite sign the paint is attracted to the object &
covers it without wastage.

15. Bibliography
1. Modern’s ABC of physics.
2. Pradeep Fundamental Physics.
3. Dinesh A to Z of Physics.
4. Comprehensive Physics.
5. Neelam’s Physics
6. Comprehensive Practical Physics.
7. N.C.E.R.T. Physics.
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