Phys2120 Spring 2017 Practice Exam 1. Chapters Name

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1 Name 1. Two point charges are 4 cm apart. They are moved to a new separation of 2 cm. By what factor does the resulting mutual force between them change? 2. An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be: 3. Two point charges each have a value of 30.0 mc and are separated by a distance of 4.00 cm. What is the electric field midway between the two charges? (k e = N m 2 /C 2 ) 4. Two point charges are separated by 10.0 cm and have charges of and 2.00 µc, respectively. What is the electric field at a point midway between the two charges? (k e = N m 2 /C 2 ) 5. The number of electric field lines passing through a unit cross sectional area is indicative of: a. field direction b. charge density c. field strength d. charge motion 6. The electric field associated with a uniformly charged hollow metallic sphere is the greatest at: a. the center of the sphere b. the sphere s inner surface c. infinity d. the sphere s outer surface 7. A charge Q accumulates on the hollow metallic dome, of radius R, of a Van de Graaff generator. A probe measures the electric field strength at various points outside the sphere surface. If the probe is initially at a distance 3R from the sphere's center and then is moved to 4R, by what factor will the electric field reading change? 8. Two point charges, separated by 1.5 cm, have charge values of +2.0 and 4.0 µc, respectively. What is the value of the mutual force between them? (k e = N m 2 /C 2 ) 9. An initially uncharged hollow metallic sphere with radius of 5 cm has a small object with a charge of +10 µc carefully placed at the center of the sphere through a hole in the latter s surface. With the charge in place, what charge is now present on the outside surface of the sphere? 10. An initially uncharged hollow metallic sphere with radius of 5 cm has a small object with a charge of +10 µc carefully placed at the center of the sphere through a hole in the latter s surface. What charge resides inner surface of the sphere? 1

2 11. A ping-pong ball covered with a conducting graphite coating has a mass of kg and a charge of 4.0 µc. What electric field directed upward will exactly balance the weight of the ball? (g = 9.8 m/s 2 ) 12. Two point charges are placed along a horizontal axis with the following values and positions: +3.0 µc at x = 0 cm and 7.0 µc at x = 20 cm. At what point along the x axis is the electric field zero? 13. Two charges, +Q and Q, are located two meters apart and there is a point along the line that is equidistant from the two charges as indicated. Which vector best represents the direction of the electric field at that point? E B E C E A + Q Q 14. Electrons in a particle beam each have a kinetic energy of J. What is the magnitude of the electric field that will stop these electrons in a distance of 0.1 m? (e = C) 15. Q 1 has 50 electric field lines radiating outward and Q 2 has 100 field lines converging inward. What is the ratio Q 1/Q 2? 16. If the distance between two negative point charges is increased by a factor of three, the resultant potential energy is what factor times the initial potential energy? 17. A proton ( C) moves 10 cm on a path in the direction of a uniform electric field of strength 3.0 N/C. How much work is done on the proton by the electrical field? 18. A proton ( C) moves 10 cm along the direction of an electric field of strength 3.0 N/C. The electrical potential difference between the proton s initial and ending points is: 19. If an electron is accelerated from rest through a potential difference of V, find its approximate velocity at the end of this process. (e = C; m e = kg) 20. Three capacitors of 1.0, 1.5, and 2.0 F are connected in series. Find the combined capacitance. 21. If three 4.0-µF capacitors are connected in parallel, what is the combined capacitance? 22. A F capacitor is attached to a 20-V power supply. How much energy is stored in the capacitor? 23. A uniform electric field, with a magnitude of 600 N/C, is directed parallel to the positive x- axis. If the potential at x = 3.0 m is V, what is the potential at x = 1.0 m? 2

3 24. Two capacitors with capacitances of 1.0 and 0.50 F, respectively, are connected in series. The system is connected to a 100-V battery. What charge accumulates on the 1.0- F capacitor? 25. A point charge of +3.0 C is located at the origin of a coordinate system and a second point charge of 6.0 C is at x = 1.0 m. At what point on the x axis is the electrical potential zero? 26. If C = 36 µf, determine the equivalent capacitance for the combination shown. C 2C C 2C 27. If C 1 = 25 µf, C 2 = 20 µf, C 3 = 10 µf, and V 0 = 21 V, determine the energy stored by C 2. C 1 V 0 C 2 C Four identical 1 mf capacitors are connected together electrically. What is the least possible capacitance of the combination? 29. Four identical 1-mF capacitors are connected together electrically. What is the greatest possible capacitance of the combination? 30. A pair of parallel plates, forming a capacitor, are connected to a battery. While the capacitor is still connected to the battery maintaining a constant voltage, the plates are pulled apart to double their original distance. What is the ratio of the final energy stored to the original energy stored? 31. A metallic conductor has a resistivity of m. What is the resistance of a piece that is 30 m long and has a uniform cross sectional area of m 2? 32. A 60-W light bulb is in a socket supplied with 120 V. What is the current in the bulb? 33. A resistor is connected to a battery with negligible internal resistance. If you replace the resistor with one that has twice the resistance, by what factor does the power dissipated in the circuit change? 3

4 34. A wire carries a steady current of 0.1 A over a period of 20 s. What total charge passes through the wire in this time interval? 35. If a lamp has resistance of 120 when it operates at 100 W, what is the applied voltage? 36. If a lamp has a resistance of 120 when it operates at 100 W, what current does it carry? 37. A solar panel measures 80 cm 50 cm. In direct sunlight, the panel delivers 3.2 A at 15 V. If the intensity of sunlight is W/m 2, what is the efficiency of the solar panel in converting solar energy into electrical energy? 38. A high-voltage transmission line carries A at V. What is the power carried by the line? 39. A high-voltage transmission line carries A at 700 kv for a distance of 100 miles. If the resistance in the wire is 1 /mile, what is the power loss due to resistive losses? 40. A tungsten wire is used to determine the melting point of indium. The resistance of the tungsten wire is at 20 C and increases to as the indium starts to melt. tungsten = ( C) 1. What is the melting temperature of indium? 4

5 KEY positive 3. zero N/C 5 c. field strength 6. d. the sphere s outer surface 7. (3/4) N 9. d. +10 µc µc N/C cm 13. Vector E A N/C 15. 1/ / J V m/s F F J V C m µf mj 28. 1/4 mf mf 30. ½ A C V A % MW MW C 5

AP physics B web review ch 15 electric forces and fields

Name: Class: _ Date: _ AP physics B web review ch 15 electric forces and fields Please do not write on my tests Multiple Choice Identify the choice that best completes the statement or answers the question.