PHY 2092-E3
Experiment 1
Electrostatics
Report Author: *Your name*
Performed: *Month* *day*, *year*
Submitted: *Month* *day*, *year*
Lab Partner: *Your partner’s name*
Instructor: Annelisa Esparza
Introduction
1
Data
Table 1: Data for Part 1
Color of Pad
Trial 1 (Volts) Trial 2 (Volts) Trial 3 (Volts) Trial 4 (Volts) Average
(Volts)
White
3
3
2
2
2.5
Blue
-4
-4
-4
-4
-4
Both
-1
-1
-1
-1
-1
Both
0
0
0
0
0
(Touching)
Table 2: Data for Part 2
Charge Source
Electrometer Reading
Side near to first sphere
-15
Side far from Sphere
15
Side far from sphere after grounding
0
2
Data Analysis
Table 2: Images in the Experiment with the corresponding technical name
File Name
Technical Name
Image 1 a
The Faradays Ice Pail
Image 1 b
Electrometer
Image 1 c
Wands-blue and white
Image 1 d
Aluminium covered wand
Image 1 e
Electrostatic voltage source
(EVS)
Image 1 f
Hook up wires
Image 1 g
Alligator clips
Table 2: Videos in the experiment with the corresponding procedure number and description.
File Name
Procedure number
Description
Pt 1 a
Part 1; step 3
The blue and white wands
were rubbed and each
lowered separately without
touching the shield.
Pt 1 b
Part 1; 5
The blue and white wands
are rubbed together and the
white want put into the
pail. The white wand is
waved in air severally and
3
again introduced to the
pail.
Pt 1 c
Part 1; 9
The white and blue wands
were rubbed together and
introduced to the pail
touching each other.
Pt 1 d
Part 1;3
The white and blue wands
were rubbed together and
only the blue wand put into
the pail with the other hand
touching the shield.
Pt 1 e
Part 1;9
Both blue and white wands
are rubbed together and
introduced into the pail
touching each other and
separated inside the pail
not to touch each other.
Pt 2 a
Part 2; 3
The wand is rubbed against
the pail shield and used to
determine the charge on
each of the sides of the
sphere
Pt 2 b
Part 2;6
A spare wire is used to
4
touch the farthest end of
one of the spheres from the
other. The spare wire is
removed and immediately
a wand used to find the
charge on that point where
the spare wire touched.
Discussion
The physics of this experiment can be described by two terms; induction and triboelectrification.
As detailed in the experiment videos, the disks on the wands are made of different materials.
When rubbed together, the two materials gain opposite electrostatic charges. The white wand has
a material that becomes positively charges when rubbed against the blue wand. The blue want
gain a negative charge. During rubbing, thermal energy causes electrons to be lost by a material.
After four trials, the charges on the white and blue wands are averaged to obtain a more accurate
and precise value. A +2.5 volt is charges on the white wand and a -4-charge charged on the blue
wand. This supports the hypothesis that the white wand is positively charged and the blue wand
negatively charged. The variations in the charge measured on the wands is due to errors in the
experiment. Intrinsic systemic errors due to secondary effects like loss of charge due to
movement of wands through air which could reduce the charge. This error is proven when the
white wand is waved in air. The wand losses its charge.
When the two wands are rubbed together and dipped to the pail without touching, the resulting
5
charge is -1. However, when the wands are dropped touching each other the resultant charge
becomes zero. This means there is a neutralizing effect and the electrometer cannot find a
polarity. This further implies that the net sum of charges is zero, what is lost by one is gained by
the other.
Humid air drains charged particles from the wands. It is the source of error. Waving the wands in
air is similar to grounding them only that the “waving in air” is not as effective as using the pail
shield. Grounding takes off the extra charge or adds the lost charge making a grounded material
neutral.
Charging by induction is different from triboelectrification. One sphere is connected to a 2000
volts source. The second sphere is placed a distance of 5cm from the first. The charges on the
first sphere cause an induced charge on the second sphere. Like charges repel and hence charges
similar to the charge on the first sphere move the farthest end of the second sphere. The second
sphere is polarized. To determine the electric potential, a Faradays Ice Pail is used.
The first sphere is positively charged hence the nearest side of the second sphere is negatively
charged. Positive charges are repelled and hence the farthest point of the second sphere from the
first sphere is positively charged. The charge density is constant for the nearest and the furthest
side on the second sphere. Grounding takes away excess charge making the sphere neutral.
The website simulates the effect of placing charges at different positions to create different
electric fields.
The dipole is created as in the figure below. It is formed by placing two different charges a
distance from each other.
6
Fig 1: Electric field created by a dipole
A linear quadrupole is created by having a +2 charge at the middle and a -1 charge at the
opposite sides.
Fig 2: Electric field created by a Linear quadrupole
7
A planar quadrupole has poles placed such that a zero-charge effect is at the middle.
Fig 3: Electric field created by a Planar quadrupole
A line of positively charged particles creates an electric-field that moves outwards.
Fig 4: Electric field created by a line of similar charges
Lining up positive and negative charges on separate lines yields up a charge that travels from the
8
positive to the negative charges.
Fig 5: Electric field created by parallel two lines of similar charges
Conclusion
We conclude from part 1 that wands rubbed together gain opposite charges. Waving a charged
wand in air causes a lose of charge. The sum of the charges cancels out when the wands touch
each other. Form the induction experiment, like charges repel and unlike charges attract.
Grounding a part makes it have a zero charge. From the virtual electric field experiment, we
conclude that an electric field is usually from the positive charge to the negative charge.
9