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Physics Exam Questions (PHYS-224) - Summer 2007 - Test #1 (Chapters 25, 26, 27), Exams of Physics

Kettering UniversityPhysics

A physics exam from the university course phys-224, taught by dr. Russell during the summer 2007 semester. The exam covers chapters 25, 26, and 27, and includes multiple-choice questions related to electric fields, point charges, and gauss' law. Students are required to determine the nature of the forces between charged objects, find net electric fields, and calculate distances for various scenarios.

Typology: Exams

Pre 2010

Uploaded on 08/07/2009

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Page 2 Test #1 (chapters 25, 26, 27) PHYS-224 Dr. Russell (Summer 2007)
1. (8 pts) Consider three plastic balls (A, B, and C), each carrying a uniformly distributed unknown
charge (which may be zero), and an uncharged copper ball (D). A positive test charge (T) is strongly
repelled from A, weakly attracted to B, strongly attracted to C, and strongly attracted to D. Assume
throughout this problem that the balls are brought very close together.
a. What is the nature of the force between balls A and B? (Explain)
i. Strongly attractive
ii. Strongly repulsive
iii. Weakly attractive
iv. Neither attractive nor repulsive
b. What is the nature of the force between balls A and C? (Explain)
i. Strongly attractive
ii. Strongly repulsive
iii. Weakly attractive
iv. Neither attractive nor repulsive
c. What is the nature of the force between balls A and D? (Explain)
i. Attractive
ii. Repulsive
iii. Neither attractive nor repulsive
d. What is the nature of the force between balls D and B? (Explain)
i. Attractive
ii. Repulsive
iii. Neither attractive nor repulsive
2. (8 pts) In the figure below,
!
q1=3.5 "10#8
C,
!
q2="5.6 #10"9
C. Distances are in meters. Find the
net electric field at point P as a vector using
!
ˆ
i
,
!
ˆ
j
unit vector notation. Be sure to draw all relevant
vectors on the figure.
pf3
pf4

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Download Physics Exam Questions (PHYS-224) - Summer 2007 - Test #1 (Chapters 25, 26, 27) and more Exams Physics in PDF only on Docsity!

Page 2 Test # 1 (chapters 25 , 26 , 27 ) PHYS- 224 Dr. Russell (Summer 2007 )

  1. ( 8 pts) Consider three plastic balls (A, B, and C), each carrying a uniformly distributed unknown charge (which may be zero), and an uncharged copper ball (D). A positive test charge (T) is strongly repelled from A, weakly attracted to B, strongly attracted to C, and strongly attracted to D. Assume throughout this problem that the balls are brought very close together. a. What is the nature of the force between balls A and B? ( Explain) i. Strongly attractive ii. Strongly repulsive iii. Weakly attractive iv. Neither attractive nor repulsive b. What is the nature of the force between balls A and C? ( Explain) i. Strongly attractive ii. Strongly repulsive iii. Weakly attractive iv. Neither attractive nor repulsive c. What is the nature of the force between balls A and D? ( Explain) i. Attractive ii. Repulsive iii. Neither attractive nor repulsive d. What is the nature of the force between balls D and B? ( Explain) i. Attractive ii. Repulsive iii. Neither attractive nor repulsive

2. (8 pts) In the figure below,

q 1 = 3.5 " 10 #^8 C,

q 2 = "5.6 # 10 "^9 C. Distances are in meters. Find the

net electric field at point P as a vector using

ˆ i ,

ˆ j unit vector notation. Be sure to draw all relevant

vectors on the figure.

PHYS- 224 Dr. Russell (Summer 2007 ) Test # 1 (chapters 25 , 26 , 27 ) Page 3

3. ( 6 pts) A point charge, Q = + 5. 2 μC is at a distance d = 3 cm from an infinite plane of charge with

density! = + 6. 8! 10

  • 3 C/m 2 . At what distance x from the point charge could an electron be placed so that it would experience zero net force?
  1. ( 6 pts) A long straight line of charge, length L and charge density ", is half positive and half negative. You need to determine the electric field at point P which is a distance d from the midpoint of the line. To do so, you treat the line as a bunch of point charges for which you can add up the electric fields. a. On the picture, draw a point charge on the positive side, and draw vectors for

E and

r^ ˆ.

b. Use symmetry to determine whether the x or y components of the electric fields cancel. c. Write down an expression for the component of the electric field at point P due to a point charge segment dq in terms of dq , r , and an angle (but don’t try to combine them)

PHYS- 224 Dr. Russell (Summer 2007 ) Test # 1 (chapters 25 , 26 , 27 ) Page 5

  1. Point P is located on the surface of a ellipsoidal surface that contains several point charges inside as shown. a. ( 3 pts) Can you use Gauss’ Law to determine the electric field at the point P indicated in the figure? (If yes, what’s the answer? If no, why not?) b. ( 3 pts) Can you use Gauss’ Law to determine the net flux through the surface? (If yes, what’s the answer? If no, why not?)
  2. A thick conducting spherical shell with inner radius a = 0. 035 m and outer radius b = 0. 048 m is in a state of electrostatic equilibrium. The shell carries a total net charge of + 4. 5 nC, and the surface charge density on the outer surface is 1. 105! 10
  • 7 C/m 2 . a. ( 5 pts) What is the charge (magnitude and sign) of the point charge at the center? b. ( 3 pts) What is the electric field at a distance of 0. 046 m from the center of the conducting shell? ( show work or explain )