Download Phys 222 -1C-FALL 12

PHYS 222 EXAM #1
FALL SEMESTER 2012
Name: _____________________
Covering Unit I
No cell phone may be used during the exam
Instructions: Circle the letter corresponding to the correct answer. If you are sure that your answer is correct and it does not
match any of those given, then write your answer on the blank space in F ____.
[5] #1. A dipole is formed by two point charges, Q 1 = -11.8 C and Q2 = + 11.8 C separated by a distance of 21.5 x 10-9 m.
Determine the magnitude and direction of the electric dipole moment.
Answer: Magnitude: A. 2.54 x 10-13 C.m..
B. 3.56 x 10-13 C.m.
C. 4.42 x 10-13 C.m.
D. 5.35 x 10-13 C.m.
-13
E. 6.42 x 10 C.m.
F. _____________________________
Answer: Direction: A. From Q1 to Q2.
B. From Q2 to Q1.
For #2 and #3, use the figure at the right which represents two point charges
Q1 = -46e and Q2 = -29e, separated by a distance of 58.6 nm.
Q2
Q1
[8] #2. Determine the location where the net electric field due to Q1 and Q2 is zero?
Answer: A. 11.8 nm, right of Q2.
B. 25.9 nm, right of Q2.
C. 35.8 nm, right of Q2.
E. 58.6 nm, right of Q2.
F. _______________________
D. 40.5 nm, right of Q2.
[6] #3. Determine the force on Q1 due to Q2.
Answer: A. 2.44 x 10-11 N, toward Q2.
B. 5.16 x 10-11 N, away from Q2.
C. 8.96 x 10-11 N, away from Q2.
-11
-11
D. 11.7 x 10 N, toward Q2.
E. 12.5 x 10 N toward Q2.
F. _______________________
For Problems #4, and #5, use the figure at the right.
The figure represents a solid sphere, with radius 22.0 cm, concentric
with a spherical shell of radius 38.0 cm. The solid sphere has a
charge of –13.8 C on it, and the outer shell has a net charge
of +21.8 C on it.
[5] #4. The surface charge density on the outer shell is
Answer:
A. +9.52 C/m2.
B. +10.4 C/m2.
F. ___________________
C. +12.0 C/m2.
D. +16.8 C/m2.
E. +22.5 C/m2.
[8] #5. The magnitude and direction of the electric field at 30.0 cm from the center is
Answer:
A. 1.38 x 106 V/m, radially inward.
B. 5.50 x 10 6 V/m, radially inward. C. 8.06 x 10 6 V/m, radially inward.
D. 9.44 x106 V/m, radially outward.
E. 11.2 x10 6 V/m, radially inward.
F. _______________________
Q1
For Problems #6 and #7 use the figure at the right.
Q2
Point charges Q1 and Q2 are located at two vertices of an equilateral triangle. Point P is the third vertex.
The length of each side of the triangle is 28.0 cm. Q1 = +26e, and Q2 = -14e.
[8] #6. The electric potential at point P is ___________. (Assume that the potential is zero at infinity.)
Answer: A. -26 nV. B +37 nV.
C. -62 nV .
D. -48 nV.
E. +72 nV.
.
F. _______________________
P
[8] #7. Point charge, Q3 = +7e, is now placed at point P. Determine the potential energy of the configuration formed
by Q1, Q2 and Q3. (Assume that the potential energy is zero at infinity.)
Answer:
A. -2.31 x 10-25 J.
B. -3.11 x 10-25 J.
C. -3.70 x 10-25 J.
D. -4.31 x 10-25 J.
E-4.81 x 10-25 J.
F. __________
[12] #8. The electric potential in a region of space is given by V = ( - 48.2 V/m3)x3 - ( 18.4V/m2)y2 + (12.1V/m)z. Determine the
electric field in the form E = Exi + Eyj + Ezk at the point (-1.0 m, +1.0 m, 2.0 m).
Answer:
A. E = (-306 V/m)i + (81.0 V/m)j - (34.4 V/m)k.
B. E = (-560 V)i + (710 V)j - (41.2 V)k..
C. E = 144 V/m)i + (36.8 V/m)j - (12.1 V/m)k.
D. E = (175 V/m)i - (44.8 V/m)j - (15.1 V/m)k.
E. E = (187 V/m)i - (50.8 V/m)j + (18.1 V/m)k.
F. ________________________
[6]#9. -38.0 nC of charge is uniformly distributed throughout a spherical volume of radius 34.0 cm.
How much charge is contained in a region of radius 23.0 cm concentric with the charge distribution?
Answer: A. -11.8 nC. B. -14.1 nC. C. -17.2 nC. D. -19.7 nC. E. -22.8 nC.
F. ________________
PHYS 222 EXAM #1 Fall Semester 2011
ABC
Name: _____________________
[6] # 10. Determine the electric flux through the Gaussian surface shown below by the broken line.
-15e
-12e
-13e
+12e
Answers:
A. +3.81 x 10-7 N.m2/C.
B. +1.27 x 10-7 N.m2/C.
-9
2
E. +3.62 x 10 N.m /C.
F. _____________________
+18e
C. +5.43 x 10-8 N.m2/C.
D. +9.05 x 10-8 N.m2/C.
[6] #11. Two masses m1= 48.6 kg and m2 = 156.4 kg are a distance of 3.8 cm apart. What is the gravitational force that they exert on
each other?
Answers:
A. 1.35 x 10-4 N.
B. 1.47 x 10-4 N.
C. 3.51 x 10-4 N.
D. 3.75 x 10-4 N.
E. 4.62 x 10-4 N.
F. _____________________
[10] #12. Circle the letter corresponding to the FALSE statements. (There are more than 1 false statements.)
A. The force on a positively charged particle that is in an electric field is in the same direction as the electric field at that point.
B. A -15e point charge that is located at a point 15 cm from the center of spherical shell that has a charge of +15e and radius 28 cm
will feel an attractive force of magnitude F = 2.58 x 10-25 N.
C. It is important to choose the shortest path between two points when calculating the work done on a charged particle by an
electric field, since the work done by the electric field depends on the path taken and we always want the path that gives the lowest the
potential energy.
D. If an object is located at the bottom of an 8 mile deep vertical hole that is drilled into the earth's crust, its weight is more than
what it would be on the earth's surface at the top of the hole.
E. Where electric field lines are very close together the electric field at that location is very weak compared to where they are far
apart.
[24] #13. The figure shows a long thin non-conducting rod of length 12 cm which has a charge of -26e spread uniformly on its surface.
Determine the electric field at point P, 5.0cm on the perpendicular bisector of the rod. (Hint: The steps below can be of help to you. )
[4](i) The charge density of the rod is __________________________
Y-axis
6.0 cm
[4](ii) Write the magnitude of dQ in terms of a tiny length dy on the y axis and the charge
density on the rod.
dQ =
0
[3](iii) Based on symmetry considerations, which component of the electric field at P is zero?
Answer_____________________________
-6.0cm
[10](iv) Determine the magnitude of the nonzero component of the electric field at P.
[3](v) On the figure draw an arrow at point P to show the direction of the electric field at that point.
5 cm
X-axis
P