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Unformatted text preview: PHYSICS 122 PRACTICE HOUR EXAM §PBIN§ 2006 .2.
 in the diagram, we have a spherical conducting shell (inner radius a and outer radius b) which
carries a total charge —2q 0 . At the center of the hollow shell is a point charge + q o.
(10 pts) (a) Determine the charge distribution on the spherical shell.
Justify your reasoning and give the principles you are using. (10 pts) (b) Find expressions for the electric field in the regions r<a,
a<r<b and b<r. That is, in the cavity, within the conductor and outside the spherical shell. Justify your answers clearly, showing your reasoning . Express your answers in terms of r, a, b and g o . ”
ll. in the figure below, two uncharged conductors of identical mass and shape are suspended
from the ceiling by nonconducting strings. The conductors are now given charges q1=Q
and (12:30. (7 pts) (a) _After charging, which of the angles 91 and 02 that the strings make with the
vertical is larger, or are they equal ? Explain. The two conductors are now brought together and made to touch. g6 pts) (b) Which of the two new angles 9’1 and 9'2 is larger, or are 1/9 “\
they equal ? Explain. [‘21 rah
(7 pts) (0) How do the angles 9’1 and 9’2 compare with the old q,=o J . q‘fo angles 91 and 92 ? Explain. lll. .
Two identical capacitors are connected in parallel. initially they are charged by a battery to a
potential V0 and each capacitor acquires a charge 00. The battery is then disconnected. A
dielectric material (K=4) is now inserted between the plates of gig of the capacitors. Lg? pts) (a) Determine the charge on each capacitor, in terms of Q0 , after the dielectric has
been inserted. g} 56’ pts) (b) Determine the new potential difference across the plates of each capacitor after
the dielectric has been inserted. Express your answer in terms of V0 gig pts) (c) How much work had to be done to insert the dielectric ? Express your answer in
terms of V0 and 00 m Explanations are reguired for full credit. . _______._...._._.__._._..__.
IV.MULTIPLE CHOICE ’l. A 2—meter stick is parallel to a uniform 200 MC electric field. The potential difference between its am
is: a) o b) 1.6 x10'17V c) 3.2 x10'17V d) 100 v e) 400 v 2. Copper contains 8.40x1028 free electrons per cubic meter. A copper wire of cross—sectional area
1 mm2 carries a current of 1.0 A . The electron drift velocity is approximately a) 3x108 m/s b) 103 m/s 0) 1 m/s d) 10'4 m/s e) 10‘23 m/s
3. Of the following, the copper conductor that has the least resistance is : a) thin, long and hot b) thick, short and cool 0) thick, long and hot d) thin, short and cool e) thin, short and hot 4. Choose the correct statement:
a) A proton tends to go from ‘a region of low potential to a region of high potential. 10. b) The potential of a negatively charged conductor must be negative.
0) If E = 0 at a point Pthen Vmust be zero at P.
d) If V= O at a point Pthen E must be zero at P. e) None of the above are correct. Charges Q, Q, and q are placed at the vertices of an equilateral triangle as shown. The total force
exerted on the charge q is: a) toward charge Q q b) toward charge Q \ c) away from charge Q x ' /
d at right angles to the linejoining Q and Q "QQ‘r—ﬂ—‘GDQ parallel to the line joining Q and —Q Two wires are made of the same material and have the same length but different radii.
They are joined end to end and a potential difference is maintained across the '
combination. Of the following, the quantity that is the same for both wires is: b) current 0) current density e) none of the above a) potential difference
d) electric field A battery is used to charge a parallelplate capacitor, after which it is disconnected. Then the plates
are pulled apart to twice their original separation. This process will double the:
a) capacitance surface charge density on each plate b) c) stored energy d) electric field between the two plates
) e charge on each plate The two charges Q are fixed at the vertices of an equilateral triangle with sides of length a.
If k=1/47r80,, the work required to move q from the other vertex to the center of the line joining
the fixed charges is: L P Q a Q a) zero b) KQq/a c) qu/a2 d) 2qu/a e) ﬁqu/a An ordinary light bulb is marked “60 watt, 120 volt” . lt’s (heated) resistance is:
a) 600 b) 1200 c) 1800 d)24OQ e) 150 Charge is distributed uniformly on the surface of a large flat plate. The electric field 2 cm from the
plate is 30 N/C. The electric field 4 cm from the plate is: a) 120 N/C b) 80 WC 0) 30 WC 8) 7.5 N/C d) 15 N/C ...
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This test prep was uploaded on 04/16/2008 for the course PHYS 132 taught by Professor Pompi during the Spring '08 term at Binghamton University.
 Spring '08
 Pompi

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