negatively charged object near the knob, the positive charges in the leaves with flow up to the knob
due to attraction of opposite charges. This causes the leaves to reduce in amount of repulsion and
come closer together. If a neutral object is brought near the knob of the electroscope, there will be no
change.
3. When a glass rod is rubbed with silk, it becomes positive and the silk becomes negative—yet both
attract dust. Does the dust have a third type of charge that is attracted to both positive and negative?
Explain.
There is not a third charge. The reason the dust could stick to either a positively or negatively
charged surfaces is because the dust itself is polarized. So the more negative charges on the dust will
attract to the positively charged glass rod, and at the same time the more positive charges on the
polarized dust will attract to the negatively charged silk.
4. Can you explain the attraction of water to the charged rod in the figure below? [6]
The chemical formula for water us H2O. Meaning the water molecule is polarized. The hydrogen is
slightly more positive and the oxygen is slightly more negative. So when the rod is brought close to
the water, the water molecules oppositely charged ends are attracted to it.
Figure 11. Water flowing out of a glass pipette
changes its course when a charged rod is
brought close to it [7].
5. Bio-Medical major? What kind of electricity can human body generate? Please think outside the
box – beyond chemical reactions.
The human body generates electricity in many ways. One being the neurons that “fire” in the brain.
With over 80 billion neurons which produce 0.085 watts of power. Enough to power a small light
bulb or charge an iPhone! Also in the blood stream humans generate more electricity than needed to
power a pacemaker! More outside of the box, the human body generates electricity outside of the
body itself. When exercising with machinery, we create electricity through the machine. And last but
certainly not least, the human body can generate electricity with its feces and waste products. As our
feces can be utilized as a fertilizer and also food for certain organisms, there is a nice chain reaction
with the energy we give off through our waste products.
7. References
1. Electrostatics: Charging Objects by Friction, Lab Manual, University of Virginia,
http://people.virginia.edu/~ral5q/classes/phys6263/fall15/Lab01.pdf
2. Brain, Ghani & Roland, Sabrina, Charging by Friction, student group report, grade 9,
http://electricalcharge.blogspot.com/2012/07/0-0-1-224-1281-aliciasumendapyahoo.html
3. PhET Interactive Simulations Project, University of Colorado,
https://phet.colorado.edu/sims/html/balloons-and-static-electricity/latest/balloons-and-staticelectricity_en.html
4. Online Gallery for this Class,
http://www.sponsorschoose.org/colleges/asuphysics/en/vw/creative.challenge.lab.1.electrostatics
5. Anrophysics, International Baccalaureate Physics,
https://www.patana.ac.th/secondary/science/anrophysics/unit2/commentary.htm
6. OpenStax, Rice University, https://cnx.org/contents/8vWesjNz@4/Conductors-and-Insulators
7. Function Space, http://functionspace.com/topic/3810/Why-is-a-stream-of-water-attracted-by-charged-rod
8. TodayIFoundOut.com, http://www.todayifoundout.com/index.php/2013/07/how-the-human-bodygenerates-electricity
9. SanDiego State University, Physics Course, http://sdsuphysics.org/physics180/physics180B/Topics/electromagnetism/images_em/electrostatics1_s.jpg
10. ReadOrRefer.com, http://www.readorrefer.us/article/Electrostatics--frictional-electricity_523
11. RoyMechx.com, http://www.roymech.co.uk/Related/Electrics/electrostatics.html
12. Phun Physics, http://phun.physics.virginia.edu/demos/electrostatics.html
13. Tutor Vista http://physics.tutorvista.com/electricity-and-magnetism/electric-charge.html
8. Acknowledgments: This Lab is based on original materials developed by Dr. Bruce Johnson in
1999 and updated by Steven Hoke in 2014. Dr. Koushik Biswas, Dr. Bin Zhang, and Dr. Brent Ross
Carroll contributed to the discussion.
9. Credits: Numerous materials developed at various schools and organizations, including MIT,
University of Virginia, etc. were used to leverage the best resources on the topic. Students are
strongly encouraged to submit their materials and get citation credits: names will be mentioned in the
final Lab manual, which you can cite on your resume.
10. Appendix: Supplemental Materials
Here are some supplemental schematic diagrams that you can insert into the right place in
your report template (give an appropriate figure caption):
[8] - go here to learn more
[9] - Go here to learn more
[10] - go here to learn more
Courtesy of Rice University [5]
Charging by induction. (a) Two uncharged
or neutral metal spheres are in contact with
each other but insulated from the rest of the
world. (b) A positively charged glass rod is
brought near the sphere on the left,
attracting negative charge and leaving the
other sphere positively charged. (c) The
spheres are separated before the rod is
removed, thus separating negative and
positive charge. (d) The spheres retain net
charges after the inducing rod is removed—
without ever having been touched by a
charged object.
Charging by induction,
using a ground connection.
(a) A positively charged rod
is brought near a neutral
metal sphere, polarizing it.
(b) The sphere is grounded,
allowing electrons to be
attracted from the earth’s
ample supply. (c) The
ground connection is
broken. (d) The positive rod
is removed, leaving the
sphere with an induced
negative charge.
Check this site: a great example of creative teaching: professors from University of Virginia are are
giving demonstrations to school students as a part of an outreach program. If there were videos of
various demonstrations posted, any students around the world could have enjoy learning physics.
You are strongly encouraged to design and include your own experiments (preferably, with videos)
[12]
6/29/99 LAM, adjusted 1/25/2016 SAH