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Unformatted text preview: A)
B) The cavity destroys the planar symmetry. To recover symmetry
imagine there are two charge distributions. 1) a positively
charged plane without a cavity and 2) a negatively charged
sphere. Find E for each separately and add them together. C)
D)
E) Version 1 Page 12 19. Two charged particles of identical mass, m, are fired straight at each other from a great
distance. The particles have identical speed v, but one particle has charge Q and the
other has charge 3Q. How close will they come to each other, i.e. what is their
minimum separation? Here, k is the Coulomb constant.
A) 5kQ 2
Total momentum of this system is zero, so the particles
2mv 2
will both be momentarily stationary when they are at
B) 3kQ
closest approach.
2
5mv
C) kQ
2mv
D) 3kQ 2
17 mv 2
E) 3kQ 2
mv 2 20. How much charge is contained within a cubical volume 2 meters on a side if the electric
ˆ
ˆ
field is given (in N/C) by E ( x, y, z) 2 xi 1.5 ˆ 6k . The cube is located with one
j
corner at the origin and with edges along the +x, +y, and +z directions.
(2,2,2)
Y (0,0,0) .
Z
X A)
B)
C)
D)
E) 0C
8.5 x 1010 C
1.4 x 1010 C
5.1 x 1011 C
2.1 x 109 C Version 1 Page 13 The y and z components of the electric
field are constant and thus create zero
flux as they go in one side and out the
other. Only the x component will
create a net flux. Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20. B
B
C
E
C
B
D
B
E
A
A
A
A
C
B
C
C
C
E
C Version 1 Page 14...
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 Spring '08
 DaveWinn
 Physics

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