Final Exam: Potential Short Answer Questions
PHY 110
(1) Your friend claims to have measured an attractive force between two positively charged
spheres to be 12 N when they are 5 m apart.
Your friend then claims that the force is 24
N when the spheres are 10 m apart.
List and briefly describe three reasons why your
friend’s claims must be wrong. One of your three points must be quantitative.
1.
Coulombs law, the distance has to be
squared
2.
like charges repel each other
3.
force decreases as the spheres move farther
apart
(2) Suppose you have two, identical socks that repel each other with a certain force.
You
move the socks so they are three times as far apart as they were originally, but the force
between them stays the same. (A) How could the magnitude of the charges change so that
the force remains constant and the socks remain identical?
Provide a quantitative answer.
(B) Now let the charges remain the same, and let the force decrease as you separate the
socks.
Does the potential energy of the system increase or decrease?
Why?
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 Fall '07
 LEVIN
 Charge, Force, Light, Electric charge, 5 m, 10 m, sparks, socks.

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