# Lab 200 - Electrostatics -- Electric Charge and Force

```Physics Laboratory Report
Title: Electrostatics – Electric Charge and Force Lab number: 200
Name: Chandru Vasudevan
Group ID: 7
Date of Experiment: _02/03/2022_
Date of Report Submission: _02/08/2022_
Course &amp; Section Number: PHYS121A006
Instructor’s Name: Topu, Saha
Partners’ Names: Joshua Villanueva, Nicholas Zubrzycki, and Thomas
O’ Mullan
1. INTRODUCTION (5 points)
1.1
OBJECTIVES
i
To demonstrate electrostatics qualitatively by exploring electric charges produced by friction and their
interaction.
ii
To understand conduction and induction to electrically charge an object.
iii
To qualitatively demonstrate electric force between charged objects.
1.2
THEORETICAL BACKGROUND
i When objects are charged without contact with a charge source, the process is known as charging
by induction. This process primarily works with conductors such as metals. As a negatively charged
object (rod) is brought near the neutral metal sphere (not in touch), some of free electrons in the
sphere move away from the rod and stay the other side. As a result, the part of the sphere nearest
the rod becomes positively charged and the opposite part negatively charged.
ii A charged object will attract a neutral object by the process of electrical polarization. For example,
a balloon negatively charged after rubbed with hair attracts pieces of paper (insulator) which are
electrically neutral (Figure 4). When a negatively charged object is brought close to an isolated,
neutral insulator, the electrons in the atoms of the insulator will be pushed slightly away from the
charged object, and the positive nuclei will be attracted slightly toward the negatively charged object.
It is called that the balloon has induced polarization in the paper (insulator), but the net charge in the
paper is still zero, which means the paper is still neutral.
iii Insulators hold on to their electrons very tightly. Charge redistribution still happens but on a much
smaller scale. Electrons move only within atoms themselves, thus pointing in the same direction when
placed near a charged object. If the charged object is positive, then the electrons face the object,
while if it is negative then the electrons point away. This re-orientation of atoms is called polarization.
iv Coulomb’s Law:
1 The first quantitative investigation of this electric force was made by Charles Coulomb, and
it is found that the magnitude of the electric force between two-point charges A and B
separated in the distance of r is given by Fe=ke(|qs|* |qt|)/r2 where ke =8.9876 &times; 109 Nm2/C2 is
called the Coulomb constant and qs, and qt, are charges of two electrically charged objects.
2 EXPERIMENTAL PROCEDURE (5 points)
✔ Since the experimental procedure followed in the conduction of this lab was the same as specified in the
lab manual, the experimental procedure will not be rewritten.
3 RESULTS (30 points in total)
3.1
EXPERIMENTAL DATA (15 points)
✔
Experiment 1:
•
Charging - The charged PVC rod attracted the quarter-inch paper squares on the table.
•
Discharging - The Neutral PVC rod did not attract the quarter-inch paper squares on the table.
✔
Experiment 2:
•
The negatively charged PVC rod was attracted to the insulated plastic straw.
Uncharged
Uncharged Metal
Plastic Straw
Acrylic Rod
Plastic Straw
(Conductor):
Rubbed with
Rubbed with
(Insulator):
Wool:
Wool:
Uncharged
Plastic Straw:
Plastic Straw
Rubbed with
Wool:
Acrylic Rod
Rubbed with
Wool:
✔
✔
✔
✔
✔
4
✔
No Interaction
Repelled
Attracted
Attracted
Attracted
Repelled
Repelled
Attracted
Attracted
Attracted
Attracted
Experiment 3:
Glass
PVC
Acrylic
✔
No Interaction
Fur
Negative
Negative
Negative
Silk
Positive
Negative
Negative
Wool
Positive
Negative
Positive
Experiment 4:
•
Charging by Conduction: After touching the pith ball with the Positively charged Fun Fly Stick, the
pith ball is now being repelled and moving away from the rod. We attained similar results when
using instead the Negatively charged PVC Pipe. Before contacting the pipe, the pith ball was
being attracted, but afterward it was being repelled.
•
Charging by Induction: When moving the Negatively charged PVC pipe underneath the pith ball,
the pith ball was attracted to the pipe. We attained similar results when using instead the
Positively charged Fun Fly Stick. When positioning the Stick directly underneath the pith ball, the
pith ball was attracted to the Stick.
Experiment 5:
•
As the Fun Fly Stick was brought closer to the pith ball, its relative angle to the vertical post
holding it up decreased as it was repelled.
Extra Activity 1:
•
As the distance between the Fun Fly Stick and the empty soda can decreased, the horizontal
speed of the Can increased. This meant that when the form of charging turned from induction to
conduction and the Fun Fly Stick made physical contact with the Can, the speed of the can
increased much more.
Extra Activity 2:
•
The pith ball moved in a periodic manner between the soda can and the Fun Fly Stick.
Extra Activity 3:
•
The NE Lamp lit up when holding the Fun Fly Stick close to but not touching the positive terminal
of the bulb. When the distance between the NE Lamp and the Fun Fly Stick decreased, the
intensity of the bulb’s light output increased. This meant that when the form of charging turned
from induction to conduction and the Fun Fly Stick made physical contact with the NE Lamp, the
intensity of light coming from the bulb increased.
ANALYSIS and DISCUSSION (35 points)
Experiment 1:
•
When the PVC rod was continually rubbed against the wool cloth, the PVC pipe, having an
intrinsic tendency to become negatively charged as described by the Triboelectric Series, lost
some of its electrons to the wool which became positively charged. As such, when the PVC rod
was brought close to the neutral small pieces of paper and aluminum sheets, the protons within
those uncharged pieces became attracted to the negative PVC pipe, both creating a positive
dipole facing the PVC rod and allowing themselves to be attached to it. This also occurred with
the Acrylic Rod, albeit with a negative dipole on the small pieces of paper and aluminum sheets,
as the Acrylic Rod has an intrinsic tendency to become positively charged as described by the
Triboelectric Series.
•
When the charged rods encountered our hands, however, the connection of our hands to the rest
of our body, which is connected to the ground, provided a pathway for electrons or protons in the
ground to travel through our body and to the stick, thus negating its charge and bringing it back to
✔
✔
✔
✔
being neutral and uncharged. This is the same principle that occurs when the rod encounters a
metal surface. The surface is connected to the ground, and therefore provides a pathway
wherewith electrons or protons can travel to the positively charged rod and match its positive
charge. Thus, we were able to demonstrate electrostatics qualitatively by exploring electric
charges produced by friction and their interaction.
Experiment 2:
•
When a negatively charged PVC rod was brought close to one end of an insulated plastic straw it
began to attract the straw. This is simply since the straw becomes polarized and forms a positive
dipole toward the PVC rod, and therefore was attracted to it. The metal platform on which it rests,
however, is connected to the ground, which is an infinite reservoir of electric charges. Protons
within the ground are thus able to establish some sort of pathway between themselves and the
PVC rod through the metal platform. This means that the metal itself is also attracted to the straw.
This same principle applies when substituting the negatively charged PVC rod for a positively
charged Acrylic Rod. Moreover, the same principle of attraction carries through to substituting the
rods for another straw. The charged straw once again attracts both the uncharged insulator straw
and the metal holder for the same reasons as the previous two rods. However, when the insulator
straw becomes charged, this force of attraction turns into one of repellence. This is since both
straws have the same charge on them, and therefore by the fundamental principles of
electrostatics, must repel. The same theory applies for the PVC rod, as its tendency to become
negatively charged matches with the tendency of the plastic straws to become negatively charged
according to the Triboelectric Series. However, since the Acrylic Rod, by the same Series, has an
intrinsic tendency to become positively charged, it attracts the negatively charged insulator plastic
straw. We did run into some issues when trying to test whether a charged Acrylic Rod on the
metal platform would repel or attract another charged Acrylic Rod. Theory suggests that these two
would repel, but instead we found them to consistently be attracting each other. Our explanation
for this phenomenon is that the Acrylic Rod on the metal platform is not as insulator as the plastic
straw, and therefore becomes neutralized upon contact with the grounded metal. This would
therefore cause the formerly charged Acrylic Rod to become polarized and become attracted to
the charged Acrylic Rod. Thus, we were able to understand conduction and induction to
electrically charge an object.
Experiment 3:
•
In order to attain our results, we placed an Acrylic Rod charged by wool, which by common
consensus is positive, on the metal stand. Afterward, we tested the impact that each of the other
material plus rod combinations had on the acrylic rod. If the given charged rod was attracted to
the Acrylic Rod, it was negative, and if the given charged rod was repelled to the Acrylic Rod, it
was positive. Thus, we were able to demonstrate electrostatics qualitatively by exploring electric
charges produced by friction and their interaction.
Experiment 4:
•
For definition’s sake, a pith ball is a Styrofoam ball that is coated in conductive paint. Therefore,
when brought close to a charged item, the pith ball will polarize and become attracted to the
charged item under the principles of induction. However, upon contact, thereby charging the ball
by conduction, they will inherit the same charge as the charged item and begin to repel. These
principles were clearly seen in the conduction of this experiment. When either the positively
charged Fun Fly Stick or the negatively charged PVC pipe was brought close to but not touching
the ball, the ball polarized and formed a positive and negative dipole respectively toward the
charged rods, thus being attracted to them. However, when contact was made between the
negatively charged PVC pipe or positively charged Fun Fly Stick and the pith ball, a transfer of
charges occurred, and the pith ball took on either electrons or protons respectively. It therefore
became an oppositely charged to the charged rods and began to repel them. Thus, we were able
to understand conduction and induction to electrically charge an object.
Experiment 5:
•
Coulomb’s Law relates the Electrostatic Force between two particles to be directly proportional to
the magnitudes of those particles and inversely proportional to the vector distance between those
particles squared. In our case, by bringing either the positively charged Fun Fly Stick or the
negatively charged PVC pipe close to the hanging pith ball, after initially touching the ball to
provide it with a charge, an Electrostatic Force would repel the pith ball from its equilibrium point,
thus increasing the angle between itself and By measuring the vector distance between these
charged objects, as well as finding the magnitude of the charges on the pith ball and either the
positively charged Fun Fly Stick or the negatively charged PVC pipe, we would be able to
calculate the theoretical Electrostatic Force. In order to validate this theoretical value, we would
use the principles of net force and periodic motion in a free-body diagram of the pith ball to
calculate the force required to keep the pith ball. By using sch a diagram, we would be able to
calculate the amount of force required to displace the pith ball by the certain angle from the
equilibrium point. We would thus be able to successfully quantitatively demonstrate electric force
between charged objects from our qualitative analysis.
✔
Extra Activity 1:
•
As evident in Coulomb’s Law, the Electrostatic Force between two particles is inversely
proportional to the vector distance between those particles squared. This means that as the
distance between two charged particles decreases, the Electrostatic Force between them
increases. This is what we experienced when holding either the positively charged Fun Fly Stick
or the negatively charged PVC pipe close to the empty soda can. When we brought either of the
charged rods closer to the empty can, its acceleration increased, therefore reflecting a
subsequent increase in Electrostatic Force acting upon it. Thus, we were able to successfully
understand electric charges produced by friction and their interaction.
✔
Extra Activity 2:
•
As described in various places above, when the positively charged Fun Fly Stick comes into the
close vicinity of the pith ball, the ball becomes inductively polarized and attracted to the stick.
However, once the ball makes conductive physical contact with the charged rod, it inherits the
same charge as the charged rod, and begins to be repelled by the charged rod. By placing an
object such as a metal can or a human hand in the path of the repelled ball, however, we provide
an outlet for the pith ball to lose its charge and return to being neutral. Once it is neutral, it again
becomes inductively polarized to the positively charged Fun Fly Stick, and therefore attracted to it
until it once again makes conductive physical contact with the Stick, becomes charged and
therefore repels once again in the direction of the can or hand that once again grounds it. The
cycle continues, creating a periodic beat that can be heard by the contact of the pith ball against
the hand or can and the charged stick. Thus, we were able to successfully understand electric
charges produced by friction and their interaction.
✔
Extra Activity 3:
• When holding the negative terminal of the NE Lamp between our fingers, a successful connection
was made from the ground to the negative terminal. Therefore, when the positively charged Fun
Fly Stick was brought close to the positive terminal of the NE Lamp, attracted electrons from the
ground rushed through our fingers and through the negative terminal and positive terminals of the
bulb to neutralize the Fun Fly Stick. In doing so, they simultaneously provided a pathway of low
resistance for an electric circuit to be formed, as the electrons carried the consistent positive
charges of the Fun Fly Stick back to the ground. Thus, we were able to successfully understand
electric charges produced by friction and their interaction.
5 CONCLUSIONS (10 points)
✔ Through the conduction of this experiment, we were able to successfully demonstrate electrostatics
qualitatively by exploring electric charges produced by friction and their interaction, understand
conduction and induction to electrically charge an object, and qualitatively determine the electric force
between charged objects.
```