Unit 6 – Sticky Tape Post Lab
L1
1. Summarize Data / Observations
Prepare a whiteboard of your data by building a table to summarize the interactions of the object.
Write if the object tested attracted (A), repelled (R), or had no interaction with the object tested (N).
Interaction with the…
OBJECT
TOP TAPE (T)
BOTTOM
TAPE (B)
FOIL (F)
PAPER (P)
T (TOP)
B (BOTTOM)
F (FOIL)
P (PAPER)
2. Develop a Descriptive Model…
What patterns do you observe in the data? Which interactions seem key to understanding
the observations?
Unit 6 - Thomson Model of the Atom
R2
J. J. Thomson performed experiments with cathode rays in an attempt to understand electricity –
which was still a mystery in the late 1800s. Review the website A Look Inside the Atom
(http://www.aip.org/history/electron/jjhome.htm) to find the conclusions that Thomson and other
physicists drew regarding the mysterious cathode rays.
Thomson’s 1897 Experiments - state the conclusions Thomson drew from each of his famous
cathode ray experiments:
1. First Experiment: Thomson directed the beam at an electrometer and tried to separate the
evidence of charge from the path of the beam. What connection did Thomson find between
charge and the cathode rays? Was the charge positive or negative?
2. Second Experiment: Thomson tried passing the cathode ray through an electric field. How did
cathode ray beam behave when it passed through an electric field? What did he conclude after his
second experiment?
3. Third Experiment: Thomson did some careful measurements on how much the path of the
cathode ray was bent in a magnetic field and how much energy they carried. From this work
Thomson could describe the mass/charge ratio of the cathode ray particles. What amazing result
did Thomson find?
Thomson’s Atomic Model: Thomson presented three hypotheses from his experiments. Only two
were accepted by physicists – in fact the third was shown to be wrong! From the first two came a
model of the atom known as the Plum Pudding model. Complete the atom drawing below to
illustrate Thomson’s plum pudding model. Explain how this fits with his observations.
3. Constructing an explanatory microscopic model.
 Model must include some internal structure to account for existence of charge.
L2
 Assume each atom contains both _______________________and _____________________
charges that normally cancel each other out.
 Thomson proposed that only the _____________________ charges are free to ____________
 These negative charges are much _____________________ than an _________________ and
are a negligible part of its _________________.
 Thomson model – massive positive _______________ with small number of mobile,
negatively charged particles called _________________________.
“Plum pudding” model:
Bowls of pudding represent _____________________ _____________________, which attract the
________________________ ______________________, represented by raisins.
__________________________ of raisins to some bowls is ________________________ than to
others, and the raisins can ________________ from one bowl to another due to differences in
attraction. Since raisins also __________________ one another, you cannot cram too many raisins
into the same bowl of pudding.
4. Application of Thomson model to sticky tapes. How do the sticky tapes become charged?
Based on our findings, the figure below might represent a layer each of atoms in the top and bottom
tapes:
When two objects of different substances come into contact:
 Some _____________________________ move from one substance to the other, based on
relative attractions of the positive cores of the two substances  some ‘raisins’ move from one
bowl to another.
 If objects are quickly separated, an ____________________ of electrons remains in one object,
counterbalanced by a ______________________ of electrons in the other  one set of bowls is
now ‘raisin-rich’, while the other is ‘raisin-poor’.
 This microscopic imbalance of charges translates to an overall macroscopic
____________________
 Top tape becomes ____________________ charged since ____________________ transfer to
bottom tape.
 Overall number of electrons does not change, just their distribution on the tapes.
L3
 _______________________ atoms have the same amount of (+) and (-) charge
 “Bowls” on _______________ side of tape have ____________________ attraction for electrons
than do “bowls” on _____________________ side of tape
Key points:
 Charge is _____________________ (can only be transferred, not created or destroyed)
 On the microscopic level, an ____________________ of charge leads to an overall macroscopic
_________________ on an object.
 Charge itself is not a substance, but is a __________________ of particles (cores and electrons)
that determines the strength of their electrical interactions.
5. Applying the Thomson model to conductivity (descriptive model)
Electric field can cause electrons to move from one core to another in __________________.
The same electric field does not result in movement of electrons in _____________________.
Attraction of positive __________________ to ________________ is weaker in metals.
6. Applying Thomson model to interaction between charged & neutral objects. (visual model)
In neutral foil and paper, electrons are equally distributed between atoms and homogenously
dispersed within each atom.
Foil (conductor)
When positively charged tape is brought near foil:
 Electrons move from __________ to __________ toward the side of the foil closest to the tape.
 The side of foil nearest the positive tape is relatively _____________________
 The positive tape has polarized the foil -> electrons are no longer evenly __________________
 Attraction between (+) top tape and (-) side of foil is _______________ than the repulsion
between top tape and (+) side of foil because distance is smaller
Paper (insulator)
When positively charged tape is brought near paper:
 Electrons shift _________________ the atoms so they are no longer symmetrically arranged
(electrons shifted toward one side of atom).
 Sides of atoms in paper nearest the (+) tape become slightly ________________ charged.
 _______________________ attraction of paper to (+) top tape
 Polarization is less pronounced because electrons are not a s free to _____________ about
(electrons stay in the atoms)
Behavior of Foil and Paper with Charged Tapes
R3
Neither foil (metal atoms) nor paper (nonmetal atoms) would attract each other.
But foil and paper are both attracted to both charged tapes (top and bottom).
Several atoms from the paper and foil are drawn below. The atoms on the left have no charged
object near them. The atoms on the right are next to a top tape (+ charge).
Add force vectors between the metal (foil) atoms and the top tape in the first row to show the
attraction between the foil and the tape. Then do the same for the paper and the tape in the second
row. Be sure the size of the vectors show the relative strengths of the attractions.
Now draw the electrons in each atom “bowl” to show their arrangements when no charged object is
near and then when a charged object is brought near.
Metal (Al Foil)
no charged object near
Nonmetal (paper)
no charged object near
Metal (Al Foil)
top tape near
Nonmetal (paper)
top tape near
Why would these arrangements of electrons produce the observed attractions?
How might we apply this model to compounds?