General Physics II (PHYS 104) Exam 2: March 21, 2002

Transcription

1 General Physics II (PHYS 104) Exam 2: March 21, 2002 Name: Multiple Choice (3 points each): Answer the following multiple choice questions. Clearly circle the response (or responses) that provides the best answer to the question. If you desire, neatly and briefly show any calculations or reasoning off to the side. This work may be considered in the evaluation of the exam. 1. Two identical aluminum objects are insulated from their surroundings. Object A has a net charge of excess electrons. Object B is grounded. Which object is at a higher potential? a) A b) B c) Both are at the same potential. d) Cannot be determined without more information. 2. A dielectric material such as paper is placed between plates of a capacitor which are maintained at a constant potential difference. What happens to the amount of charge on the plates when the dielectric material is inserted? a) No change. b) Increases. c) Decreases. d) Reduces to zero. 3. A 12 resistor. How many electrons flow through the wire in 1.0 min? a) 1.5X1019 b) 2.5X1019 c) 3.5X1019 d) 4.5X When a light bulb is connected to a 4.5 V battery, a current of 0.16 A passes through the bulb filament. What is the resistance of the filament? A) 440 B) 28 C) 9.3 D) 1.4 E) A 4-A current is maintained in a simple circuit with a total resistance of 2. How much energy is dissipated in 3 seconds? A) 3 J B) 6 J C) 12 J D) 24 J E) 96 J 6. What is the potential at a distance of 5.0X10-10 m from a nucleus of charge +60e? a) 140 V b) 170 V c) 210 V d) 250 V

2 7. The resistivity of most common metals a) remains constant over wide temperature ranges. b) increases as the temperature increases. c) decreases as the temperature increases. d) varies randomly as the temperature increases. Use the following to answer questions 8-12: The sketch below shows cross sections of equipotential surfaces between two charged conductors that are shown in solid black. Various points on the equipotential surfaces near the conductors are labeled A, B, C,..., I. 8. What is the direction of the electric field at B? A) toward A D) into the page B) toward D E) up and out of the page C) toward C 9. What is the magnitude of the electric field at point A? A) 10 V/m B) 25 V/m C) 30 V/m D) 75 V/m E) 100 V/m 10. A point charge gains 50 J of electric potential energy when it is moved from point D to point G. Determine the magnitude of the charge. A) 1.0 C B) 1.3 C C) 25 C D) 50 C E) 130 C 11. How much work is required to move a 1 C charge from B to D to C? A) J D) J B) J E) zero joules C) J 12. At which of the labeled points will an electron have the greatest potential energy? A) A B) D C) G D) H E) I

3 Questions and Problems: Provide clear and logical answers to the following questions. Where calculations are required, neatly show all work. Be sure that your answers have the correct units. Questions are worth 10 points each. 1) Two ends of a wire carrying 0.6 A of current are maintained at a potential difference of 12 V. Determine the length of copper wire (resistivity 1.7X10-8 current flows through 2) Two parallel plates, separated by 0.20 m, are connected to a 12-V battery. An electron released from rest at a location 0.10 m from the negative plate. When the electron arrives at a distance m from the positive plate, a) how much potential energy does the electron loose? b) what is the speed of the electron at this location?

4 3) Two charges of opposite sign and equal magnitude Q = 2.0 C are held 2.0 m apart as shown in the figure. a) Determine the electric potential produced at the P by the two charges. b) Determine the electric potential produced at R by the two charges. 1.0 m c) What is the work done by the electric force in moving a charge of q = 0.5 C from point R to point P? R

5 8. What is the equivalent capacitance of the combination of capacitors shown in the circuit? A) 0.37 µf B) 3.3 µf C) 4.6 µf D) 0.67 µf E) 2.1 µf

6 2. A 10.0-µF capacitor is charged so that the potential difference between its plates is 10.0 V. A 5.0-µF capacitor is similarly charged so that the potential difference between its plates is 5.0 V. The two charged capacitors are then connected to each other in parallel with positive plate connected to positive plate and negative plate connected to negative plate. a) How much charge flows from one capacitor to the other when the capacitors are connected? b) What is the final potential difference across the plates of the capacitors when they are connected in parallel?

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