PHYSICS
ART
INTEGRATIO
N PROJECT
TO ESTIMATE THE CHARGE
INDUCED ON EACH OF THE
TWO IDENTICAL
STRYOFOAM (OR PITH)
BALLS SUSPENDED IN A
VERTICAL PLANE BY
MAKING USE OF
COULOMB’S LAW
S.T.SAHANA
D.NANDHIKA
R.RASHMIKA
R.KAVIYA DHARSHINI
XII A1
Coulomb
Coulomb graduated in
November 1761 from École
royale du génie de Mézières.
Over the next twenty years he
was posted to a variety of
locations where he was
involved in engineering -
structural, fortifications, soil
mechanics, as well as other
fields of engineering. His first
posting was to Brest but in
February 1764 he was sent to
Martinique, in the West Indies,
where he was put in charge of
building the new Fort Bourbon
and this task occupied him until
June 1772.
On his return to France, Coulomb was sent to Bouchain.
However, he now began to write important works on
applied mechanics and he presented his first work to the
Académie des Sciences in Paris in 1773. In 1779 Coulomb
was sent to Rochefort to
collaborate with the Marquis de Montalembert in
constructing a fort made entirely from wood near Ile d'Aix.
During his period at Rochefort, Coulomb carried on his
research into mechanics, in particular using the shipyards
in Rochefort as laboratories for his experiments.
Upon his return to France, with the rank of Captain, he was
employed at La Rochelle, the Isle of Aix and Cherbourg. He
discovered an inverse relationship of the force
COULOMB’S LAW
In 1785 Augustine de Coulomb investigated the attractive
and repulsive forces between charged objects,
experimentally formulating what is now referred to as
Coulomb’s Law: “The magnitude of the electric force that a
particle exerts on another is directly proportional to the
product of their charges and inversely proportional to the
square of the distance between them.” Mathematically, this
electrostatic F acting on two charged particles (q1, q2) is
expressed as
Coulomb's inverse-square
law, or simply
Coulomb's
law, is an experimental
law of physics that
calculates the amount of
force between two
electrically charged
where r is the separation distance particles
between at the
rest.
objects and
k is a constant of proportionality, called the Coulomb
constant,
𝑘 = 9. 0 * 109 N.𝑚2/𝐶2. This formula gives us the
magnitude of the force as well as direction by noting a
positive force as attractive and a negative force as
repulsive. Noting that like charges repel each other and
opposite charges attracting each other, Coulomb
measured the force between the objects, small metal
coated balls, by using a torsion balance similar to the
balance used to measure gravitational forces.
OBJECTIVE
To estimate the charge induced on each of the two identical
styro foam (or pith) balls suspended in a vertical plane by
making use of coulomb’s law.
MATERIALS REQUIRED
Small size identical balls (pitch or soft
plastic)
Physical balance or electronic balance
Halfmeter Scale
Cotton thread
Stand
Glass rod (or plastic rod)
Silk cloth (or wollen cloth)
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.
Surprisingly, the exact physics of the process of
charging by friction is poorly understood. However, it is
known that the making and breaking of contact
between the two materials transfers the charge.
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.
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 to the square of
the distance between the charges, and is directed
along the straight line that connects their
centers.
2. The force is proportional to the product of the
magnitude of the charges.
3. Two particles of the same 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
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 polarization.
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
polarization in the insulator, but its net charge is still zero.
The polarization 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 polarized. 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
polarized, and will now be attracted to the charged rod.
Now if we connect a conducting wire or any other
conducting material from the polarized 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.
Let the force between two stationary charges
be F
The Weight of the ball ; W=mg
The restoring force on each ball
=mgsinɵ From the diagram in the
2l
right
In triangle ACB
Let the sinɵ = X on each ball
charge
be
q1=q2=q
Then at equlilibrium
mgsinɵ = kq
×q
mg2 = 𝑥2
𝑥2
X l kq2
2 = 2lk
mgxmgx
3
2l
= 3
k
PROCEDUR
E1. Weight the mass of each identical pitch balls by
balance and note down it.
2. Tie the balls with two silk or cotton threads and suspend
at a point on a stand or a rigid support. Measure the
length of threads by half meter scale. The length of
threads should be equal. Note down the length.
3. Rub the glass rod with silk cloth and touch with both
balls together so that the balls acquired equal
charge.
4. Suspend the balls freely and the balls stay away a
certain distance between the balls when they become
stationary. Note down the distance.
5. Touch any one suspended ball with other uncharged
third ball and takes the third ball away and repeat the
step 4.
6. Touch other suspended ball with other uncharged fourth
ball and takes the fourth ball away and repeat the step
4.
OBSERVATION
1. Mass of each ball, = 200 g.
(m)
= 0.2
2. Radius of each ball, mm.
3. (r)
Length of each thread,(l) = 100
cm.
S.N CHARGE ON CHARGE ON DISTANCE
BALL BALL BETWEEN
A (q1) B (q2) THE BALLS
(X cm)
1 0.00µC 0.00 µC 0.4cm
2 1.00 µC 1.00 µC 20.8cm
3 2.00 µC 2.00 µC 26.2cm
4 2.00 µC 2.00 µC 33.0cm
CALCULATIONS
= mgx
2l
By using the
Calculate the charge in each k
3
relation
case:
1.
2
.
3
.
4
.
RESULTS
The charge on each ball is
𝑞1 = 2.6 x 10−9 C
𝑞2 = 9.9 x 10−7 C
𝑞3 = 1.41 x 10−6 C
𝑞4 = 1.99 x 10−6 C
PRECAUTIONS:-
1. The suspended balls should not be touched by any
conducting body.
2. Rub the glass rod properly with the silk cloth to produce
more charge.
3. Weight the mass of the balls accurately.
SOURCE OF ERROR:-
4. The balls may not be of equal size and mass.
5. The distance between the balls may be measured
accurately.
