PHYS 1120 Exam 3 NAME:______________________________ Spring 2008 E3.1 Third Midterm Student ID #__________________________________________________ Section number and TA Name:___________________________________ Exam Version 0001 Please do not open the exam until you are asked to. • Your exam should have 7 pages, numbered E3.1 thru E3.7. • 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: µ0 = 4π10-7 T·m/A, basic charge unit 1.6x10-19 C, ε0 = 8.85x10-12 C2/(N.m2) Magnetic field magnitude from a long straight wire Good luck!PHYS 1120 Exam 3 NAME:______________________________ Spring 2008 E3.2 Third Midterm loop Wire with current, I Circle the closest answer and Bubble in questions 1-15 ON YOUR BUBBLE SHEET! 1. A negative particle is moving up the page through a magnetic field coming out of the page. The force on the particle due to the B-field is.. A) into the page B) out of the page C) to the left D) to the right 2. Two wires in the plane of the page have the same magnitude but oppisite directions of current as shown in the diagram. What is the direction of the force ON wire 2? A) to the left B) to the right C) out of the page D) into the page 3. A wire loop is near a long, straight wire carrying a current, which is increasing, as shown. The induced current in the loop is .. A) clockwise B) counter-clockwise C) zero. 4. A particle of mass 2x10-6 kg and carrying a net positive charge of q = e (the charge of a proton), is traveling at uniform velocity, v, of 10m/s in the positive x direction perpendicular to an electric field E of 1V/m, which is in the positive y direction. A magnetic field is directed perpendicular both E and v (in the positive z direction) and cancels the electric force. What is the magnitude of the B field? A) 1.25x1014 T B) 1T C) 10T D) 0.1T E)need more information B -Q I2 I1 V E BPHYS 1120 Exam 3 NAME:______________________________ Spring 2008 E3.3 Third Midterm The following three questions refer to this situation: Two wires, one with current I1 up the page and the other with current I2 twice as large as I1, also up the page, are located in the page and pointing perpendicular to the x-axis as shown below. The three questions below ask about the magnetic field on the x-axis in the three regions: I. some finite distance to the left of the two wire (anywhere but infinity), II. somewhere in between the two wires, and III. some finite distance to the right of the two wires (anywhere but infinity). 5. In region I, the magnetic field .. A) is everywhere non-zero and pointing out of the page B) is everywhere non-zero and pointing into the page C) can be zero at some location. 6. In region III, the magnetic field .. A) is everywhere non-zero and pointing out of the page B) is everywhere non-zero and pointing into the page C) can be zero at some location. 7. In region II, if I1=1A and I2=2A and the wires are separated by 3 meters. The magnitude of the magnetic field 1 meter away from I1 is: A) 2x10-7 T B) 4x10-7 T C) 1.26x10-6 T D) zero 8. A long straight wire, carrying a current of 1.5amps, passes through the center of a circular wire loop of radius 2mm. The wire loop is in the plane of the page, the straight wire is perpendicular to the page. The magnetic flux through area enclosed by the wire loop is .. A) 1.9x10-6 T*m2 B) 1.5x10-4 T*m2 C) 1.9x10-9 T*m2 D) zero. I II III +x I1 I2 = 2I1PHYS 1120 Exam 3 NAME:______________________________ Spring 2008 E3.4 Third Midterm The next two questions refer to the RL circuit shown. Initially, the switch is open and the circuit has no current flowing. Then, at time t=0, the switch is closed. 9. Immediately after the switch is closed, the voltage across resistor is A) zero, but increasing towards 2V B) 2V, but decreasing towards zero C) the same as for the inductor D) 2V independent of time. 10. A long time after the switch has closed, and the circuit has reached steady-state, the current through the resistor is A) 20 A B) 2 A C) 0.50 A D) 0.2 A D) nearly zero. 11. Two solenoid inductors labeled 1 and 2 are made of the same type of wire and have the same radius. Solenoid 2 is three times as long and has 3 times the number of turns as solenoid 1. They both carry the same current. What is the ratio B2/B1 of the fields in each? A) 1 B) 3 C) 9 D) 27 E) None of these. 12. Which of the two solenoids in problem 11 has a larger inductance? A) Solenoid 1 B) Solenoid 2 C) they have the same inductance D) not enough information R=1 ohm L=0.1h 2VPHYS 1120 Exam 3 NAME:______________________________ Spring 2008 E3.5 Third Midterm 13. A circular loop of wire has 100 turns, an area of 0.3 m2, and has a static magnetic field of 2 Tesla perpendicular to the area. Then, the magnitude of the magnetic field begins changing with time, following the formula, . The magnitude of the induced EMF across the loop at t=1msec is: A) 300 V B) 30 kV C) 60 V D) 0.6 V E) None of these. 14. A loop of wire is placed uniform B-field that is perpendicular to the loop as shown. An electromotive force (EMF) measured in volts appears across the loop:
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