COULOMBʼS LAW VIDEO WORKSHEET
Background information on Coulomb’s Law Film
Here, manic Princeton professor Eric Rogers hosts, continually
removing and replacing his eyeglasses, ordering around lab assistants
--- he forcefully breaks a glass test tube in the hands of an assistant
to demonstrate the inelasticity of water --- and furiously pounds
equations on a blackboard (The film’s director, Leacock says the
scribblings must have lasted 45 minutes, in what must be one of the
more necessary cuts in the history of educational film.) Rogers finally
conducts an experiment with a young girl, placing her in a metal cage,
which he then charges with electricity, demonstrating through the
inverse square law that his assistant (Leacock’s trusting daughter
Elspeth) is not harmed by the charge.
PART 1 (click here to watch part 1 of video)
1. ______________ are enormously important in nature. On the
atomic scale they far outweigh any ______________.
2. Electric forces hold ________________ together and make steel
wire __________________. The electric force in the wire, Dr.
Rogers plucks, is equal to the ______________ of the hanging blocks.
3. Electric forces also hold atoms ________________and make
water difficult to ______________.
4. Electric forces hold the parts of ______________ together. The
parts include ______________ and nuclei.
5. The law of force between ______________charges must be known
to understand the models of atomic structure that scientist use.
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PART 2 (click here to watch part 2 of video)
6. At small distances electric forces compete well with
______________.
7. The exact relationship between the electric force and the distance
between the charges is:
8. Sketch the graph that shows the above exact relationship.
9. At twice the distance between two charges the electric force is
______________ as big and at ten times the distance the electric
force drops to ______________ as big.
10. The illumination of light follows the ______________ square law.
11. If you hold your hand at twice the distance from your face, your
hand will appear to be ______________ as big.
PART 3 (click here to watch part 3 of video)
12. A century after ______________ guessed at an
______________ law for gravitation, ______________guessed at a
similar law for ______________. He tested his guess with a
______________, rather like the ______________balance used for
the gravitational inverse square law test.
13. The Coulomb Law apparatus in the film consists of two
__________ balls that can be charged, a beam carrying one ball, a
spring to balance the ____________ between the balls, and a
___________ to show the stretch of the spring on a scale. Label the
various parts on the photo. The scale is already labeled.
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14. The following is a data table that will be used when Dr. Rogers
investigates the relationship between the electric force and distance.
15. The first set of data is collected as a thought experiment. Fill in
the results in the table above.
16. The metal balls are charged up using an ancient charging device
that operates by ______________ charges on the plate. Rogers gives
each ball _________________________ (the same sign of charge,
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the same amount of negative charge, the same amount of positive
charge, a different amount of charge but of different sign) and then
measures the force as a function of _____________ between the
charged balls.
17. Fill in the data table .
18. Make a sketch of the graph of the collected data.
PART 4 (click here to watch part 4 of video)
19. The experiment of this part investigates the relationship between
_________ and the product of the charge. He begins by placing
the_______ sign charge on two metal balls. One is being managed by
his assistant and the other is attached to the beam. A force
measurement is made and recorded. Record the value in the table
below.
20. To change the charge of one of the balls, Dr. Rogers uses an
identical, but uncharged ball attached to an insulated wand. He brings
the uncharged ball to the charged ball that his assistant is managing
and touches it. This action results in each ball having the __________
charge, but __________of the charge on the ball held by the
assistant. There is now a ________ % reduction in the product of the
interacting charges. Dr. Rogers then grounds the ball that is attached
to the wand. His assistant then moves the ball with half of its original
charge back into position and a force measurement is made. Record it
in the table.
21. Dr. Rogers then repeats the above procedure, resulting in another
_______% reduction of the product of the interacting charge. A force
measurement is made. Record it. The force is proportional to
________ of the charges or in other words, the force is proportional
to the product of the charges.
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22. Sketch the graph of the electric force as a function of the
product of the charges.
PART 5 (click here to watch part 5 of video)
23. Dr. Rogers argues that if Coulombʼs Law holds, then if we have a
large hollow metal ball with electric charge we find __________
electric effect inside and if there is no electric effect inside then
there must be an _________________ law force between charges.
24. When the two touching solid conductors are placed just outside
the charged hollow conductor sphere, what charges reside on them?
When the two are placed inside, what charges reside on them? To
answer these questions, simply show the charges, if any, on the spheres
as Dr. Rogers does.
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PART 6 (click here to watch part 6 of video)
25. When the two touching solid conductors just outside the sphere
are separated each has the _________amount of charge, but they are
____________ in charge. When one of these is touched to the
electroscope the leaves of the electroscope ___________ (repel,
collapse). When the other is then touched to the electroscope the
leaves ____________ (repel, collapse).
26. There is ________ electric effect inside a hollow metal charged
sphere. In fact, there is _________ shielding.
PART 7 (click here to watch part 7 of video)
27. The results of the previous experiment apply to __________
metal box. It must be _______________ and it must be a
_______________.
28. Charges on shapes other than spheres concentrate along
__________ and _____________ in such a way that they produce
exactly __________ electric force _____________. A small hole
doesnʼt matter. Even _____________ works. Any metal box, even a
____________ cage, will give complete _______________.
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PART 8 (click here to watch part 8 of video)
29. First Dr. Rogers gives his young assistant a net _________
charge.
30. Her hair, like the leaves of the electroscope, acquire a
__________charge and the individual strands of hair
_____________ each other.
31. The young assistant experiences ___________ electrical effect
inside the metal cage.
PART 9 (click here to watch part 9 of video)
32. Answer Dr. Rogerʼs question.
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