P202 Practice Exam 1 Spring 2004 Instructor: Prof. Sinova Name: Date: 1. Each of three objects has a net charge. Objects A and B attract one another. Objects B and C also attract one another, but objects A and C repel one another. Which one of the following table entries is a possible combination of the signs of the net charges on these three objects? A B C A) + + B) + + C) + D) + E) + 2. Consider three identical metal spheres, A, B, and C. Sphere A carries a charge of 2.0 µc; sphere B carries a charge of 6.0 µc; and sphere C carries a charge of +5.0 µc. Spheres A and B are touched together and then separated. Spheres B and C are then touched and separated. Does sphere C end up with an excess or a deficiency of electrons and how many electrons is it? A) deficiency, 6 10 13 B) excess, 3 10 13 C) excess, 2 10 13 D) deficiency, 3 10 12 E) deficiency, 1 10 12 Page 1
3. Four point charges, each of the same magnitude, with varying signs are arranged at the corners of a square as shown. Which of the arrows labeled A, B, C, and D gives the correct direction of the net force that acts on the charge at the upper right corner? A) A B) B C) C D) D E) The net force on that charge is zero. 4. Three charges are located along the x axis as shown in the drawing. The mass of the 1.2 µc charge is 4.0 10 9 kg. Determine the magnitude and direction of the acceleration of the 1.2 µc charge when it is allowed to move if the other two charges remain fixed. A) 2 10 5 m/s 2, to the right B) 1 10 5 m/s 2, to the left C) 7 10 4 m/s 2, to the right D) 3 10 5 m/s 2, to the left E) 4 10 6 m/s 2, to the right Page 2
5. An electron traveling horizontally enters a region where a uniform electric field is directed upward. What is the direction of the force exerted on the electron once it has entered the field? A) to the left B) to the right C) upward D) downward E) out of the page, toward the reader The figure shows a parallel plate capacitor. The surface charge density on each plate is 8.8 10 8 C/m 2. The point P is located 1.0 10 5 m away from the positive plate. 6. Which one of the following statements concerning the direction of the electric field between the plates is true? A) It points to the left. B) It points to the right. C) It points toward the negative plate. D) It points toward the positive plate. E) It points up out of the plane of the page. 7. What is the magnitude of the electric field at the point P? A) 8.8 N/C B) 88 N/C C) 1.0 10 2 N/C D) 8.8 10 2 N/C E) 9.9 10 3 N/C Page 3
8. A helium nucleus is located between the plates of a parallel-plate capacitor as shown. The nucleus has a charge of +2e and a mass of 6.6 10 27 kg. What is the magnitude of the electric field such that the electric force exactly balances the weight of the helium nucleus so that it remains stationary? A) 4.0 10 7 N/C B) 6.6 10 26 N/C C) 2.0 10 7 N/C D) 5.0 10 3 N/C E) 1.4 10 8 N/C The figure shows a parallel plate capacitor. The surface charge density on each plate is 8.8 10 8 C/m 2. The point P is located 1.0 10 5 m away from the positive plate. 9. If a +2.0 10 5 C point charge is placed at P, what is the force exerted on it? A) 0.2 N, toward the negative plate B) 0.2 N, toward the positive plate C) 5 10 4 N, toward the positive plate D) 5 10 4 N, toward the negative plate E) 5 10 4 N, into the plane of the page 10. A straight, copper wire has a length of 0.50 m and an excess charge of 1.0 10 5 C distributed uniformly along its length. Find the magnitude of the electric field at a point located 7.5 10 3 m from the midpoint of the wire. A) 1.9 10 10 N/C B) 1.5 10 6 N/C C) 6.1 10 13 N/C D) 7.3 10 8 N/C E) 4.8 10 7 N/C Page 4
11. Two point charges are arranged along the x axis as shown in the figure. At which of the following values of x is the electric potential equal to zero? Note: At infinity, the electric potential is zero. A) +0.05 m B) +0.29 m C) +0.40 m D) +0.54 m E) +0.71 m Two charges of opposite sign and equal magnitude Q = 2.0 C are held 2.0 m apart as shown in the figure. 12. Determine the magnitude of the electric field at the point P. A) 2.2 10 9 V/m B) 5.6 10 8 V/m C) 4.4 10 8 V/m D) 2.8 10 8 V/m E) zero V/m 13. Determine the electric potential at the point P. A) 1.1 10 9 V B) 2.2 10 9 V C) 4.5 10 9 V D) 9.0 10 9 V E) zero volts Page 5
14. A parallel plate capacitor with plates of area A and plate separation d is charged so that the potential difference between its plates is V. If the capacitor is then isolated and its plate separation is decreased to d/2, what happens to the potential difference between the plates? A) The potential difference is increased by a factor of four. B) The potential difference is twice it original value. C) The potential difference is one half of its original value. D) The potential difference is one fourth of its original value. E) The potential difference is unchanged. 15. The effective area of each plate of a parallel plate capacitor is 2.4 m 2. The capacitor is filled with neoprene rubber (κ = 6.4). When a 3.0-V potential difference exists across the plates of the capacitor, the capacitor stores 5.0 µc of charge. Determine the plate separation of the capacitor. A) 7.2 10 5 m B) 3.0 10 4 m C) 1.7 10 4 m D) 5.3 10 4 m E) 8.2 10 5 m 16. At which point (or points) is the electric field zero N/C for the two point charges shown on the x axis? A) The electric field is never zero in the vicinity of these charges. B) The electric field is zero somewhere on the x axis to the left of the +4q charge. C) The electric field is zero somewhere on the x axis to the right of the 2q charge. D) The electric field is zero somewhere on the x axis between the two charges, but this point is nearer to the 2q charge. E) The electric field is zero at two points along the x axis; one such point is to the right of the 2q charge and the other is to the left of the +4q charge. Page 6
Answer Key 1. D 2. D 3. B 4. B 5. D 6. C 7. E 8. C 9. A 10. E 11. B 12. B 13. E 14. C 15. E 16. C Page 7