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Practice Exam 2 - Foundations of Physics I | PHYS 2306, Exams of Physics

Virginia Polytechnic Institute and State University (Virginia Tech)Physics
Prof. Yangsoo Kim

Material Type: Exam; Professor: Kim; Class: Foundations of Physics I; Subject: Physics; University: Virginia Polytechnic Institute And State University; Term: Spring 2009;

Typology: Exams

Pre 2010

Uploaded on 04/09/2009

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PHYS2306: Practice Test 2
For the best result of the test, you need to understand completely the example problems in the lecture and the
homework problems. This practice test serves as a complementary tool. Please note that the actual test will not
necessary have the same questions as in this practice test. This practice test is to help you to study in
preparation of the upcoming test. DO NOT assume that there will be the same questions in the real test.
1. A particle with mass m and, charge ٛq is projected with speed v0 into the region between two parallel
plates as shown. The potential difference between the two plates is V and their separation is d. The
change in kinetic energy of the particle as it traverses this region is:
A) ٛqV/d B) C) qV D) E) none of these
2. The flux of the electric field ˆ
ˆˆ
(24 N/C) (30 N/C) (16 N/C)ijk++ through a 2.0 m2 portion of the yz
plane is:
A) 32 N ⋅ m2/C B) 34 N ⋅ m2/C C) 42 N ⋅ m2/C D) 48 N ⋅ m2/C E) 60 N ⋅ m2/C
3. Consider Gauss law: 0
/.EdA q
ε
⋅=
∫JG JG
v Which of the following is true?
A)
E
JG
must be the electric field due to the enclosed charge
B) If q = 0 then 0E=
JG
everywhere on the Gaussian surface
C) If the three particles inside have charges of +q, +q and −2q, then the integral is zero
D) On the surface
E
JG
is everywhere parallel to dA
J
G
E) If a charge is placed outside the surface, then it cannot affect
E
J
G
on the at any point on the surface
4. A point charge is placed at the center of a spherical Gaussian surface. The electric flux ΦE is changed
if:
A) the sphere is replaced by a cube of the same volume
B) the sphere is replaced by a cube of one-tenth the volume
C) the point charge is moved off center (but still inside the original sphere)
D) the point charge is moved to just outside the sphere
E) a second point charge is placed just outside the sphere
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Download Practice Exam 2 - Foundations of Physics I | PHYS 2306 and more Exams Physics in PDF only on Docsity!

PHYS2306: Practice Test 2

For the best result of the test, you need to understand completely the example problems in the lecture and the homework problems. This practice test serves as a complementary tool. Please note that the actual test will not necessary have the same questions as in this practice test. This practice test is to help you to study in preparation of the upcoming test. DO NOT assume that there will be the same questions in the real test.

  1. A particle with mass m and, charge ٛ q is projected with speed v 0 into the region between two parallel plates as shown. The potential difference between the two plates is V and their separation is d. The change in kinetic energy of the particle as it traverses this region is:

A) ٛ qV / d B) C) qV D) E) none of these

  1. The flux of the electric field (24 N/C) i ˆ^ + (30 N/C) ˆ j + (16 N/C) k ˆthrough a 2.0 m^2 portion of the yz plane is: A) 32 N ⋅ m^2 /C B) 34 N ⋅ m^2 /C C) 42 N ⋅ m^2 /C D) 48 N ⋅ m^2 /C E) 60 N ⋅ m^2 /C
  2. Consider Gauss law: (^) ∫ E d A ⋅ = q / ε 0.

JG JG

v Which of the following is true? A) E

JG

must be the electric field due to the enclosed charge B) If q = 0 then E = 0

JG

everywhere on the Gaussian surface C) If the three particles inside have charges of + q , + q and − 2 q , then the integral is zero D) On the surface E

JG

is everywhere parallel to d A

JG

E) If a charge is placed outside the surface, then it cannot affect E

JG

on the at any point on the surface

  1. A point charge is placed at the center of a spherical Gaussian surface. The electric flux Φ E is changed if: A) the sphere is replaced by a cube of the same volume B) the sphere is replaced by a cube of one-tenth the volume C) the point charge is moved off center (but still inside the original sphere) D) the point charge is moved to just outside the sphere E) a second point charge is placed just outside the sphere

5. A physics instructor in an anteroom charges an electrostatic generator to 25 μC, then carries it into the

lecture hall. The net electric flux in N ⋅ m^2 /C through the lecture hall walls is: A) 0 B) 25 × 10? C) 2.2 × 105 D) 2.8 × 106 E) can't tell unless the lecture hall dimensions are given

  1. Charge Q is distributed uniformly throughout an insulating sphere of radius R. The magnitude of the electric field at a point R /2 from the center is: A) Q /4πε 0 R^2 B) Q /πε 0 R^2 C) 3 Q /4πε 0 R^2 D) Q /8πε 0 R^2 E) none of these
  2. Positive charge Q is distributed uniformly throughout an insulating sphere of radius R , centered at the origin. A particle with a positive charge Q is placed at x = 2 R on the x axis. The magnitude of the electric field at x = R /2 on the x axis is: A) Q /4πε 0 R^2 B) Q /8πε 0 R^2 C) 7 Q / 18 πε 0 / R^2 D) 11 Q /18πε 0 R^2 E) none of these
  3. Positive charge Q is placed on a conducting spherical shell with inner radius R 1 and outer radius R 2. A particle with charge q is placed at the center of the cavity. The magnitude of the electric field at a point in the cavity, a distance r from the center, is:

A) Q / 4 πε 0 R 12 D) ( q + Q )/4πε 0 r^2

B) Q / 4 πε 0 ( R 1^2 − r^2 ) E) ( q + Q ) / 4 πε 0 ( R 1^2 − r^2 )

C) q /4πε 0 r^2

  1. Positive charge Q is placed on a conducting spherical shell with inner radius R 1 and outer radius R 2. A point charge q is placed at the center of the cavity. The magnitude of the electric field produced by the charge on the inner surface at a point in the interior of the conductor a distance r from the center, is:

A) 0 B) Q / 4 πε 0 R 12 C) Q / 4 πε 0 R 22 D) q /4πε 0 r^2 E) Q /4πε 0 r^2

  1. Positive charge Q is placed on a conducting spherical shell with inner radius R 1 and outer radius R 2. A point charge q is placed at the center of the cavity. The magnitude of the electric field at a point outside the shell, a distance r from the center, is:

A) Q / 4 πε 0 R 12 D) ( q + Q )/4πε 0 r^2

B) Q / 4 πε 0 ( R 1^2 − r^2 ) E) ( q + Q ) / 4 πε 0 ( R 1^2 − r^2 )

C) q /4πε 0 r^2

  1. A spherical conducting shell has charge Q. A particle with charge q is placed at the center of the cavity. The charge on the inner surface of the shell and the charge on the outer surface of the shell, respectively, are: A) 0, Q B) q , Q? q C) Q , 0 D) ٛ q , Q + q E) ٛ q , 0
  1. A parallel plate capacitor is fully charged at a potential V. A dielectric with constant κ = 4 is inserted between the plates of the capacitor while the potential difference between the plates remains constant. Which one of the following statements is false concerning this situation? A) The energy density remains unchanged. B) The capacitance increases by a factor of four. C) The stored energy increases by a factor of four. D) The charge on the capacitor increases by a factor of four. E) The electric field between the plates increases by a factor of four.
  2. A parallel plate capacitor has a potential difference between its plates of 1.2 V and a plate separation distance of 2.0 mm. What is the magnitude of the electric field if a material that has a dielectric constant of 3.3 is inserted between the plates? A) 75 V/m B) 180 V/m C) 250 V/m D) 400 V/m E) 500 V/m
  3. A uniform electric field of 8 V/m exists between the plates of a parallel plate capacitor. How much work is required to move a +20 μC point charge from the negative plate to the positive plate if the plate separation is 0.050 m? A) 0.4 J B) 1.6 J C) 8 ٛ 10?^ J D) 8 ٛ 10?^ J E) 8 ٛ 10?^ J
  4. Capacitor C 1 is connected alone to a battery and charged until the magnitude of the charge on each

plate is 4.0 × 10 −^8 C. Then it is removed from the vattery and connected to two other capacitors C 2 and C 3 , as shown. The charge ont he positive placte of C 1 is then 1.0 × 10 −^8 C. The charges on the positive plates of C 2 and C 3 are:

A) q 2 = 3.0 × 10 −-8^ C and q 3 = 3.0 × 10 −^8 C D) q 2 = 3.0 × 10 −^8 C and q 3 = 1.0 × 10 −^8 C B) q 2 = 2.0 × 10 −^8 Cand q 3 = 2.0 × 10 −^8 C E) q 2 = 1.0 × 10 −^8 Cand q 3 = 3.0 × 10 −^8 C C) q 2 = 5.0 × 10 −^8 Cand q 3 = 1.0 × 10 −^8 C

21. A 2- μF and a 1- μF capacitor are connected in series and charged by a battery. They store energies P

and Q , respectively. When disconnected and charged separately using the same battery, they have energies R and S , respectively. Then: A) R > P > S > Q D) P > R > S > Q B) P > Q > R > S E) R > S > Q > P C) R > P > Q > S

  1. To store a total of 0.040 J of energy in the two identical capacitors shown, each should have a capacitance of:

A) 0.10 μF B) 0.50 μF0.10 μF C) 1.0 μF D) 1.5 μF E) 2.0 μF

  1. An ordinary light bulb is marked "60 watt, 120 volt". Its resistance is: A) 60 Ω B) 120 Ω C) 180 Ω D) 240 Ω E) 15 Ω
  2. Suppose the electric company charges 10 cents per kW⋅h. How much does it cost to use a 125 watt lamp 4 hours a day for 30 days? A) $1.20 B) $1.50 C) $1.80 D) $7.20 E) none of these
  3. In the figure, two small concentric conducting spherical shells produce a radially outward electric field of magnitude 49,000 N/C a distance of 4.10 m from the center of the shells. If the inner shell contains a charge of -5.30 mC, find the amount of charge on the outer surface of the larger shell.

Use the following to answer questions 26-27:

Two concentric spheres are shown in the figure. The inner sphere is a solid nonconductor and carries a charge of +5.00 mC uniformly distributed over its outer surface. The outer sphere is a conducting shell that carries a net charge of -8.00 mC. No other charges are present. The radii shown in the figure have the values R 1 = 10.

cm, R 2 = 20.0 cm, and R 3 = 30.0 cm.

  1. Find the total excess charge on the inner and outer surfaces of the conducting sphere.

Answer Key

1. C

2. D

3. C

4. D

5. D

6. D

7. C

8. C

9. D

10. D

11. D

12. A

13. D

14. A

15. A

16. C

17. E

18. B

19. E

20. A

21. E

22. C

23. D

24. B

  1. 91.4 μC
    • 5.00 μC (inner surface), - 3.00 μC (outer surface)
  3. (i) 0; (ii) 2.00 × 10 6 N/C, radially outward; (iii) 0; (iv) 2.20 × 106 N/C, radially inward