Physics 202 Midterm 1 Practice Exam Name: Student ID: Section: TA (please circle): Daniel Crow Scott Douglas Yutao Gong Taylor Klaus Aaron Levine Andrew Loveridge Jason Milhone Hojin Yoo Instructions: 1. Don't forget to write down your name, student ID#, and section number. You need to do this on (this page of your test book and on your Scantron sheet as well, where you should fill in your student ID number under Identification number and your three digit section number starting with 3 under special codes). 2. Answer all multiple questions in this test book by indicating the best answer among choices. You must do this both on your test book and on your Scantron sheet. Follow instructions on the Scantron sheet on how to mark valid answers. 3. When you finish, you need to turn in both this test book and the Scantron sheet. 4. Use the blank side of question pages as additional draft spaces. An extra bank sheet is provided at the end of the test book. 5. Only one answer is allowed per problem/question/ All problems have equal weight. Constants: k e = 8.99 x 10 9 Nm 2 /C 2 1. Two small spheres attract one another electrostatically. This can occur for a variety of reasons. Which of the following statements must be true? A) at least one sphere is charged B) neither is charged C) both are charged D) both have the same charge E) None of these is correct. Page 1
2. Three charges +q, +Q, and Q are placed at the corners of an equilateral triangle as shown. The net force on charge +q due to the other two charges is A) vertically up. B) vertically down. C) zero. D) horizontal to the left. E) horizontal to the right. 3. Two charges Q 1 and Q 2 are distance d apart. If the electric field is zero at distance 3d/2 from Q 1 and d/2 from Q 2, along the line joining Q 1 and Q 2, then what is the relation between Q 1 and Q 2? A) Q 1 = 9Q 2 B) Q 1 = Q 2 /9 C) Q 1 = Q 2 /3 D) Q 1 = 3Q 2 E) Q 1 = 9Q 2 Page 2
4. In the diagram, Q 1 = 9.0 µc and Q 2 = 9.0 µc. If Q 2 has a mass of 3.0 g, a uniform electric field of 1.8 kn/c imposed in the positive y direction would give this particle an acceleration in the y direction of approximately A) zero B) 5.4 m/s 2 C) 6.8 cm/s 2 D) 4.5 m/s 2 E) 7.5 cm/s 2 5. An electron is released from rest in a uniform electric field. If the electric field is 1.25 kn/c, at the end of 20 ns the electron's velocity will be approximately A) 2.5 10 5 m/s B) 3.9 10 3 m/s C) 3.0 10 8 m/s D) 2.5 10 3 m/s E) 4.4 10 6 m/s 6. A uniform circular ring has charge Q and radius r. The magnitude of the electric field at a distance of r along the axis of the ring is E o. If the radius were to double, then calculate the new electric field at a distance of r along the axis of the ring in terms of E o. A) 0.40 E o B) 0.25 E o C) 0.50 E o D) 0.20 E o E) 0.089 E o Page 3
7. The figure shows a surface enclosing the charges 2q and q. The net flux through the surface surrounding the two charges is A) q/ 0 B) 2q/ 0 C) q/ 0 D) zero E) None of these is correct. 8. An infinitely long cylindrical shell of radius 6.0 cm carries a uniform surface charge density σ = 12 nc/m 2. The electric field at r = 10.0 cm is approximately A) 12 kn/c B) 0.56 kn/c C) 1.3 kn/c D) 0.81 kn/c E) zero 9. A solid sphere of radius a is concentric with a hollow sphere of radius b, where b > a. If the solid sphere has a charge +Q and the hollow sphere a charge of Q, the electric field at radius r, where a < r < b, is which of the following, in terms of k = (4π 0 ) 1? A) kq/r 2 B) 2kQ/r 2 C) kq/a 2 D) kq/b 2 E) kq/(b a) 2 Page 4
10. A solid spherical conductor has a radius of 15 cm. The electric field 30.0 cm from the center of this sphere has a magnitude of 800.0 N/C. What is the surface charge density σ on the sphere? A) 7.1 10 9 C/m 2 B) 1.0 10 8 C/m 2 C) 1.4 10 8 C/m 2 D) 2.8 10 8 C/m 2 E) 1.1 10 7 C/m 2 11. A charge of 2.0 mc is located in a uniform electric field of intensity 4.0 10 5 N/C. How much work is required to move this charge 20.0 cm along a path making an angle of 60.0 with the electric field? A) 0.14 J B) 0.34 J C) 80 mj D) 14 J E) 8.0 J 12. Two charges Q 1 (= +6 µc) and Q 2 (= 2 µc) are brought from infinity to positions on the x-axis of x = 4 cm and x = +4 cm, respectively. How much work approximately was done in bringing the charges together? (Round your answer to 1 significant figure) A) 2 10 6 J B) 9 10 5 J C) 20 J D) 1 J E) none of the above Page 5
13. A charge of 100 nc resides on the surface of a spherical shell of radius 20 cm. The electric potential at a distance of 50 cm from the center of the spherical shell is approximately A) 20 V B) 200 V C) 2000 V D) 20,000 V E) None of these is correct. 14. The figure shows portions of four equipotential surfaces whose potentials are related as follows: V 1 > V 2 > V 3 > V 4. The lines represent four paths (A A', B B', C C', D D') along which equal test charges are moved. The work involved can be said to be A) the greatest for path A A'. B) the greatest for path B B'. C) the greatest for path C C'. D) the greatest for path D D'. E) the same for all paths. Page 6
Use the following to answer question 15. 15. The electrostatic potential energy of the system of point charges q 1 = 1.00 µc, q 2 = 2.00 µc, and q 3 = 3.00 µc at the corners of the equilateral triangle whose side s = 30.0 cm is A) 1.10 J B) 0.990 J C) 0.631 J D) 0.330 J E) 0.123 J 16. An 80-nF capacitor is charged to a potential of 500 V. How much charge accumulates on each plate of the capacitor? A) 4 10 4 C B) 4 10 5 C C) 4 10 10 C D) 2 10 10 C E) 2 10 7 C 17. If you increase the charge on a parallel-plate capacitor from 3 µc to 9 µc and increase the plate separation from 1 mm to 3 mm, the energy stored in the capacitor changes by a factor of A) 27 B) 9 C) 3 D) 8 E) 1/3 Page 7
18. If C 1 < C 2 < C 3 < C 4 for the combination of capacitors shown, the equivalent capacitance A) is less than C 1. B) is more than C 4. C) is between C 2 and C 3. D) is less than C 2. E) could be any value depending on the applied voltage. 19. A charged capacitor has an initial electric field and potential difference V 0 across its plates. Without connecting any source of emf, you insert a dielectric (κ > 1) slab between the plates to produce an electric field and a potential difference V d across the capacitor. The pair of statements that best represents the relationships between the electric fields and potential differences is A) > ; V d > V 0 B) = ; V d > V 0 C) > ; V d = V 0 D) < ; V d > V 0 E) < ; V d < V 0 20. The capacitance of a parallel-plate capacitor is 24 µf when the plates are separated by a material of dielectric constant 2.0. If this material is removed, leaving air between the plates, and the separation between the plates is tripled, the capacitance is A) unchanged B) 16 µf C) 36 µf D) 0.14 mf E) 4.0 µf Page 8
Answer Key - Midterm1_practice 1. A 2. E 3. E 4. B 5. E 6. B 7. A 8. D 9. A 10. D 11. C 12. D 13. C 14. E 15. D 16. B 17. A 18. B 19. E 20. E Page 9