PHYS 1120 Exam 2 NAME Student ID Section number and TA Name Exam Version 0002 Please do not open the exam until you are asked to Your exam should have 7 pages numbered E2 1 thru E2 7 This exam consists of 15 multiple choice questions worth 5 points each and a long answer section worth 25 points for a total of 100 points Write your answers in the space provided on each page for the written question Use the back of the page if needed Circle the correct letter for the multiple choice questions SHOW YOUR WORK ON THE WRITTEN QUESTIONS Full credit will be given only for the correct answer accompanied by your reasoning PLEASE 1 2 3 4 Print your name on each page in the space provided Print your student Identification Number on the page above Bubble your name ID and exam version number on the bubble sheet provided Write the name of your TA neatly in the big blank space at the bottom of the bubble sheet TA s names are Charles Bailey Jeremy Brown Craig Hogle Daniel McKinnon and Youngwoo Yi I recommend Don t waste time erasing on the written problems Just put a line through defective reasoning Ask for more paper if needed At the end of the exam check that you have completed all the questions By handing in this exam you agree to the following statement On my honor as a University of Colorado Student I have neither given nor received unauthorized assistance on this work Signature Possibly useful information k 9 0x109 N m2 C2 basic charge unit 1 6x10 19 C 0 8 85x10 12 C2 N m2 Electrostatic potential of a point charge chosen to be zero at infinite distance Electric field magnitude from a surface charge density Good luck Spring 2008 E2 1 Second Midterm V2 PHYS 1120 Exam 2 NAME Circle the closest answer and Bubble in questions 1 15 ON YOUR BUBBLE SHEET 1 A total current I is flowing through a copper bar that has been machined as shown in the following figure In which region is the drift velocity largest A A B B C C D Drift velocity is the same in all three regions The following two questions refer to this situation Two capacitors one of capacitance C1 0 5 microfarads and the other C2 2 microfarads are both charged by attaching them across batteries C1 is attached across a 2 volt battery C2 is attached across a 1 volt battery C1 2V 2 The ratio of the energies stored in the two capacitors is C2 1V A 2 B 1 2 C 4 D 1 e None of these 3 The two capacitors shown above have identical dimensions same plate separation d and same plate area A but one of the two capacitors has an air gap and the other has a plastic dielectric between the plates Which capacitor has the dielectric A Capacitor 1 B Capacitor 2 C impossible to tell without further information 4 Two parallel metal plates of area 1 m2 are separated by a distance of 1 millimeter and have no dielectric between them The plates are charged by applying 1000 volts between them The magnitude of the electric field between the plates is A 106 V m B 1000 V m C 8 85x10 15 V m D 8 85x10 9 V m E None of these Spring 2008 E2 2 Second Midterm V2 PHYS 1120 Exam 2 NAME The following two questions refer to this situation Consider two identical positively charged particles each has charge Q The two particles are placed a distance R apart in empty space Assume that the potential is defined to be zero at infinity Q Q R 5 The electric potential at the point exactly half way between the particles is A B C D E zero 6 The potential energy of the system is assume voltage 0 and PE 0 at infinity A B C D E zero As is shown in the figure to the right charge of Q is located a distance r from the origin and at 45 degrees above the x axis Similarly a charge of Q is located the same distance r from the origin but at 45 degrees below the x axis Assume that the potential is zero at infinity 7 The voltage at the origin is A B C D zero E none of these 8 A positive charge of 1 Coulomb is placed at rest near another positive point charge Q The voltage is 375 V at the initial location of the 1 C charge The 1 C charge is released from rest and is repelled from the charge Q and after some time it is very far away and in a region of space where the voltage is very close to zero At that later time the kinetic energy of the 1 C charge is nearly A 375 J B 375 J C 187 J D 187 J E zero Spring 2008 E2 3 Second Midterm V2 PHYS 1120 Exam 2 NAME 9 A capacitor of C 4 microFarads is charged by placing it across a 5 volt battery switch at position a in the figure The capacitor is then connected across an R 20 Ohm resistor and is allowed to discharge switch at position b in the figure Immediately after connecting the resistor across the capacitor the current through the resistor is A zero B 250 milliAmp C 100 Amp D 8x10 5 Amp E None of these 10 For the loop labeled L in the figure which of the following is a correct Kirchoff potential equation A B C D E L None of the above Spring 2008 E2 4 Second Midterm V2 PHYS 1120 Exam 2 NAME 11 An electron current of I 15 0 amps flows for exactly 180 seconds How many electrons flow through the wire in that 180 second interval A 2 8x1020 B 1 60x10 19 C 1 69x1022 D 2700 E None of these 12 A resistor is made from copper wire with a resistivity of 1 57x10 8 Ohm meter The wire is 2 meters long and has a circular cross section of radius 0 1 millimeter What is the resistance A 0 25 Ohm B 1E 4 Ohm C 1 0 Ohm D 3 14 Ohm E None of these The following three questions refer to the circuit shown to the right 13 In the circuit all the resistors have the same resistance Which statement is correct A B C D E B A The same current flows through each resistor Each resistor has the same voltage drop Each resistor has the same power dissipation None of the above All of the above C V 14 If each resistor in the circuit above is 10 Ohms then the total circuit resistance is A 30 Ohms B 20 Ohms C 15 Ohms D 3 33 Ohms E None of these 15 The ratio of the power dissipated by resistor A to the power dissipated by resistor B PA PB is A 1 4 Spring 2008 B 1 2 C …
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