Physics Review Chapter 17 & 18 Name: Date: Period: 1. What sentence best characterizes electron conductors? a. They have low mass density b. They have high tensile strength c. They have electric charges that move freely d. They are poor heat conductors 2. What happens when a rubber rod is rubbed with a piece of fur, giving it a negative charge? a. Protons are removed from the rod b. The fur is also negatively charged c. The fur is left neutral d. Electrons are added to the rod 3. An attracting force occurs between two charged objects when a. charges are of unlike signs b. charges are of like signs c. charges are of equal magnitude d. charges are of unequal magnitude 4. A repelling force occurs between two charged objects when a. charges are of unlike signs b. charges are of like signs c. charges are of equal magnitude d. charges are of unequal magnitude 5. Which sentence best characterizes electric insulators? a. Charges on their surface do not move b. they have high tensile strength c. Electric charges move freely on them d. They are good heat conductors 6. When a glass rod is rubbed with silk and becomes positively charged, a. electrons are removed from the rod b. protons are added to the silk c. protons are removed from the silk d. the silk remains neutral 7. Which of the following transfers charge most easily? a. nonconductors b. conductors c. semiconductors d. insulators 8. If a positively charged glass rod is used to charge a metal bar by induction, a. the charge on the bar will be equal in magnitude to the charge on the glass rod b. the charge on the bar must be negative c. the charge on the bar must be positive d. the charge on the bar will be greater in magnitude than the charge on the glass rod 9. The process of charging a conductor by bringing it near another charged object and then grounding the conductor is called a. charging by conduction b. charging by polarization c. neutralization d. charging by induction
10. Electric charge is a. found only in a conductor b. conserved c. found only in insulators d. not conserved 11. Unlike insulators, conductors can be charged by a. grounding b. induction c. polarization d. conduction 12. A surface charge can be produced on insulators by a. grounding b. induction c. polarization d. contact 13. When a charged body is brought close to an uncharged body without touching it, a(n) charge may result on the uncharged body. When a charged body is brought into contact with an uncharged body and then is removed, a(n) charge may result on the uncharged body. a. negative, positive b. positive, negative c. induced, residual d. residual, induced 14. A balloon has a negative charge of 3.5 µc. How many excess electrons are on the balloon? a. 3.5 x 10 6 b. 2.2 x 10 13 c. 3.9 x 10 16 d. 3.8 x 10 24 15. What determines the direction of the force between two charges? a. the signs of the charges b. the magnitude of the charges c. the distance between the charges d. Coulomb s law 16. Which of the following statements concerning electric field lines is false? a. Electric field lines cannot cross each other. b. Electric field lines must begin at a positive charge and end at a negative charge. c. Electric field lines are always tangent to the direction of the electric force. d. Electric field lines do not actually exist. 17. Two parallel plates are oppositely charged. The left plate is negative and the right plate is positive. In which direction does the electric field point? a. right b. left c. cannot be determined 18. What is the electric potential energy between the electrons of an oxygen molecule and its protons, if the are 6.0 x 10 11 m apart? a. 2.46 x 10 16 J b. 2.46 x 10 16 J c. 1.89 x 10 16 J d. None of these
19. The energy associated with a charge due to its position relative to a source of electric force is. a. electric potential b. Voltage c. electric potential energy d. potential difference 20. A battery is a source of which of the following? a. Capacitance b. Voltage c. dielectric d. induction 21. When charging a capacitor a. it must be attached to a battery. b. charges move back from one plate to another through the circuit until both plates are uncharged. c. charges move from one plate to another until equal and opposite charges accumulate on the plates. d. it cannot be connected to a material that conducts. 22. A capacitor consists of two metal plates; is stored on one plate and is stored on the other. a. negative charge; positive charge b. potential energy; kinetic energy c. potential difference; internal resistance d. residual charge; induced charge 23. To decrease the capacitance of a capacitor that is disconnected from the battery, you could a. decrease the distance between the plates b. increase the distance between the plates c. ground the capacitor so electrons move away from the plate 24. A uniform electric field with a magnitude of 500 N/C is directed parallel to the positive xaxis. If the potential at x = 5 m is 2500 V, what is the potential at x = 2 m? a. 1000 V c. 4000 V b. 2000 V d. 4500 N V = E d E( d f d i ) 500 (2m 5m) = 1500V C
Problems: 1. An electron and a proton are separated by a distance of 1.0 x 10 19 m. a. What is the PE of the proton if the separation is doubled? PE = Kq 1 q 2 /r = ½ the original b. How much work must you do on the proton to double the separation? PE = Kq 1 q 2 / r = W = [9.0e9(1.6e19) (1.6e19)]/2.0e19 = 1.152e9 J c. What is the V for the proton if the separation is doubled? V = PE/q = 1.152e9/1.6e19 = 7.2e9 V 2. What is the electric field half way between a proton and an alpha particle (charge 2e) that are separated by a distance of 3.0 x 10 6 m? r 1 = r/2 E = E 1 E 2 Kq 1 /r 1 2 K Kq 2 /r 1 2 = K/r 1 2 (e2e) = [9.0e9/(1.5e6)] 2 (1.6e191.6e19) = 640 N/C 3. Find the electric force on a 60 nc charge located at (0,3) if there are two charges of 40.0 nc, one located at (2,0) and the other at (0,0). Where would you place the 60 nc charge so it is in equilibrium? Omit 4. Calculate the net charge on a substance consisting of a combination of 7.0 x 10 13 protons and 4.0 x 10 13 electrons. Calculate the electric potential at a point midway between the protons and electrons if they are separated by 2.0 x 10 5 m. Assume all protons are in one small clump and all electrons in another. 7.0 4.0 = 3e13 protons If 1 proton = 1.6e19 C then 3e13 * 1.6e19 C = 4.8 µc 5. A Van de Graaff generator is charged so that the electric field at its surface is 3.0 x 10 4 N/C. What is the electric force on a proton released at the surface of the generator? Eq= Fe 4 = 3.0e (1.602e 19 ) = 4.806e 15 N 6. A capacitor has an electric field of 3.4 x 10 5 N/C between its plates. What is the distance between the plates if there is a 12 V potential difference in the capacitor? V = Ed d = V E 12 = 3. 529e 5 3.4e 5 m
2 µc = q 2 5 µc = q 3 2 µc = q 1 7. At q3, draw the field vectors for q1 and q2. 8. Draw the net field vector at q3. 9. If q3 is doubled to 10 µc, how does the Electric Field at q3 change? (2 2) = 2 Doubles 1 10. The electric field is 10 N/C. Draw a field vector on the capacitor. 11. Place an A at the place where the electric potential is 8 V relative to the plate. V = Ed = d = V/E = 8/10 = 0.8 m anywhere between the plates from side 12. How much would the potential change if the A moved 10 cm closer to the negative plate? V = Ed = 10 * (0.1) = 1V Given the proximity of charged rubber (negative charge) and glass rods (positive charge), how would the following respond? To the rubber rod To the glass rod 13. Small stream of water attract attract 14. charged balloon repel attract 15. Small piece of paper attract attract 16. Uncharged pith ball attract attract 17. Pith ball that was previously in contact with the glass rod attract repel