1 of 9 Exam 3, vers. 0001 - Physics 1120 - Spring, 2003 NAME_______________________________________________________ Signature_____________________________________________________ Student ID #__________________________________________________ TA’s Name(Circle one): Michael Schefferstein, Chris Keller, Paisa Seelungsawat Starting time of your Tues recitation (write time in box: 9am, 1pm, etc) Please do not open the exam until you are told to. Your exam should have 10 pages, numbered 1 thru 10. There is a blank sheet at the end for scratch. This exam consists of 25 questions, worth 4 points each for a total of 100 points. Fill in the bubble sheet with a #2 pencil. You must fill out your bubble sheet according to the following instructions or you will automatically lose 10 points. Place a check in each box on the left as you complete the instructions. Print and bubble in your name and student ID on the bubble sheet. Print and bubble in your Exam version, 0001 or 0002, in the upper left of your bubble sheet in the area marked 1234. Please leave the areas labeled Code and Date blank Erase mistakes as thoroughly as possible. Ask for a fresh bubble sheet if you fear you cannot thoroughly erase mistakes. As you take the exam, circle the correct answers on your exam as well as marking them on the bubble sheet. That way we can grade the exam, if your bubble sheet is lost. At the end of the exam, check that you have filled in the first 25 questions on the bubble sheet, with only one bubble filled in for each question. I have read and followed the instructions above. Signature______________________________________________ Possibly useful information: Coulomb's constant k = 9×109(SI units), e = 1.6×10–19 C, 1208.85 10 (SI units)−ε= ×µ0 = 4π×10–7 (SI units) Vers. 00012 of 9 1. A coil of wire with N = 2 loops is attached to a 1Ω resistor and is oriented perpendicular to a uniform magnetic field as shown. At a particular instant, the magnitude of the magnetic field is B = 0.50 T and the field is DECREASING at a rate of 0.05 T/s. The area of each loop is A = 0.50 m2. What is the magnitude of the current through the resistor? B decreasing A) 1.0 mA B) 20 mA C) 50 mA D) zero E) None of these. R= 1Ω 2. In the problem above, the direction of the current through the resistor is.. A) up ↑ B) down↓ C) current is zero 3. A hand-cranked electrical generator is attached to a resistor R. The generator is turned at a constant rate which causes an AC current to flow in the resistor. Suddenly, the value of the resistance R decreases. Does the generator get easier or harder to turn? A)Easier. B) Harder. C) No change in difficulty. 4. A step-down transformer has NP=1000 turns in the primary coil and NS=100 turns in the secondary coil. The primary side is plugged into a standard 120V AC outlet, and the secondary side is attached to a R = 10 Ω resistor. To two-place precision, what is the rms current drawn from the outlet? A) 0.24 A B) 0.12 A C) 1.2 A D) 2.4 A E) None of these. Vers. 00013 of 9 5. A solenoid has circular cross-section and radius R. The current of the solenoid is steadily increasing , creating a uniform magnetic field within the solenoid which is increasing at a steady rate, dB/dt = constant. What is the magnitude of the electric field E at a point outside the solenoid a distance r (r>R) from the center of the solenoid? A)zero B) πRdBdt2 C) RrdBdt22 D) 2πrRdBdt E) None of these. 6. An electron (q = –e) is released from rest in a region of space where there is constant, uniform, electric field GE, and a constant, uniform magnetic field GB. The electric field points up and the magnetic field points into the page in the diagram. Which, if any, of the four paths shown will the electron follow? (The four paths are in the plane of the paper.) 7. A block of mass m, with a net positive charge q, is placed on a frictionless plane inclined at an angle θ. A uniform horizontal external electric field of magnitude E is applied in the direction shown. How big does the electric field have to be so that the mass m starts to move up the incline? The E-field must be bigger than A) tanmgqθ B) qcosmgθ C) sinqmg θ D) cosmgqθ E) None of these B(in) E A) B)C) D)E) None of these is correct. θ +q, m E Rr .B increasing Vers. 00014 of 9 8. A hairdryer with resistance R is plugged into a standard 120VAC wall socket (the rms voltage is 120V). The current through the hairdryer as a function of time is shown. Note that each tick mark along the y-axis is 2 A. What is the resistance R of the hairdryer (to two-place precision)? 10 I (A) 0 -10A) 12 Ω B) 24 Ω C)17 Ω D) 0.059 Ω E) 60 Ω time 9. A long straight wire, carrying a current I, passes through the center of a circular wire loop. The wire loop is in the plane of the page, the straight wire is perpendicular to the page, and current is going into the page and is decreasing. The current induced in the wire loop is … wire loop I(in) decreasing A) counter-clockwise B) clockwise C) zero 10. As indicated in the diagram, the magnetic field in a certain region is given by ˆ(, )Bxy Ayx= where A is a positive constant. Consider the imaginary loop shown. What can you say about the current through the loop? A) The current through the loop must be zero. B) There must be a non-zero current through the loop coming out of the page. C) There must be a non-zero current through the loop going into the page. D) You can say nothing about the current through the loop, on the basis on of the information given. B y xVers. 00015 of 9 11. The diagram shows the equipotential lines of a point charge located at the origin. Note that the tic marks show 1 m spacing. What is the value of the charge? 10m 1 kV 5m 2 kV A) 1 µC B) 1 mC C) 106 C D) 3.3 × 10-10 C E) None of these 5m 10m3 kV 12. Two positive charges and a negative charge, all of equal magnitude (+Q, +Q, and –Q) are located at the three corners of a square of edge length r. The origin is the fourth corner of the square. At the origin, what is the direction of the electric field? y +Q r –Q r x E) None of these; either the field is zero, or it points in some other direction. +Q A) B) C) D) 13. The same current I is flowing through solenoid A and solenoid B, which both have circular cross section. The solenoids have the same length, but solenoid A has twice
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