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Electric Problem Set #1
1) Delicate measurements indicate that the Earth has an electric field surrounding it,
similar to that around a positively charged sphere. Its magnitude at the surface of the
Earth is about 100.0 N/C. What charge would an oil drop have, to be suspended by the
Earth’s electric field if the drop has a mass of 2.00 x 10-15 kg? Give your answer in
elementary charges.
2) An argon nucleus is placed above another argon nucleus such that it remains
suspended above it. How far apart are they?
3) 2 alpha particles are fired at each other at 0.0025c. What is their distance of closest
approach?
4) An alpha particle starts at rest between 2 parallel plates with 2000.0 V applied to it.
What speed would it have at the negative plate if a) it starts at the positive plate? B) if it
starts midway?
5) A pith ball of mass 1.0 x 10-5 kg has a positive charge of 0.40μC and is at rest. It is
slowly pulled by a string 50.0 cm through a potential difference of 800.0 V. The pith ball
is then released where it returns back to its original position. Find:
a) the work done by the string to move the pith ball
b) the average force required to perform this work
c) the kinetic energy with which the pith ball attains as it returns back to its starting
point
d) its speed upon return to the starting point
6) Two electrons are held at rest, 10-12 m apart and released. What is each of their
kinetic energy and speed at a very large distance apart?