Download Test 1

test 1
Physics 25
Name
February 20, 2013
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1. In an imaginary universe, atomic electrons have a charge of2.5 C. Two identical ions (i.e.
atoms missing one or more of these electrons) repel each other with a force of 25K N when
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held a distance of2 m apart. (K is the constant in Coulomb's law). How many electrons are
missing from this imaginary atom?
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2. Two charges are located at the vertices of a triangle as shown below. We are interested in
finding the electric field at the 3rd vertex.
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a) Draw the unit vectors ~25 and ;-32 at the 3 vertex.
b) What are the x- and y-components of ~25 and
c). What is the electric field at the 3rd vertex?
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3. A charged particle with mass 10 kg and charge 4 C is in a uniform electric field of 5 N/C. If
this particle starts from rest, how fast will it be going after it has traveled a distance of 9 m?
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4. It is found experimentally that the electric field in a certain region of the Earth's atmosphere
is directed vertically up. At an altitude of 50 m the field has a magnitude of 3 N/C and at an
altitude of 70 m the magnitude of the field is 5 N/C. Imagine a cube in space 20 m on edge,
with horizontal faces at altitudes of 50 m and 70 m. How much charge is inside this cube?
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5. A solid sphere of radi us 6 m. carries a total charge of 72 C uniformly distributed through out
the sphere.
a). Is the sphere an insulator or conductor?
b) Using Gauss' law, find the electric field at a radius of3 m.
b)
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6. a) How much work is required to move a charge of6 C from the bottom left comer of the
rectangle to the top right comer for a path along the diagonal?
b) How much work is required to move the same charge first horizontally to the location of
the 6C charge and then vertically to the top right comer?
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