PHYS 1120 Exam 2 NAME:______________________________ Spring 2008 E2.1 Second Midterm V2 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. Print your name on each page in the space provided. 2. Print your student Identification Number on the page above. 3. Bubble your name, ID, and exam version number on the bubble sheet provided. 4. 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, ε0 = 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!PHYS 1120 Exam 2 NAME:______________________________ Spring 2008 E2.2 Second Midterm V2 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.. 2. The ratio of the energies stored in the two capacitors is: 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. C1 2 V C2 1 VPHYS 1120 Exam 2 NAME:______________________________ Spring 2008 E2.3 Second Midterm V2 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. 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 +Q +Q RPHYS 1120 Exam 2 NAME:______________________________ Spring 2008 E2.4 Second Midterm V2 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) None of the above. LPHYS 1120 Exam 2 NAME:______________________________ Spring 2008 E2.5 Second Midterm V2 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) The same current flows through each resistor. B) Each resistor has the same voltage drop. C) Each resistor has the same power dissipation. D) None of the above. E) All of the above. 14. If each resistor in the circuit
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