Physics 1252 xam #3A nstructions: This is a closed-book, closed-notes exam. You are allowed to use a clean print-out of your formula sheet, any scientific calculator, and a ruler. Do not write on your formula sheet, except for your name: it must be handed in, signed but clean, with your exam. There is space after each question to show your work; if you need more space, you may use the back of the page, or request more paper. Please clearly indicate where your work for each problem is. Underline or draw a box around your final answer. The exam consists of four sections. Read all the questions at the start so that you can allocate your time wisely. Do easy ones first! You may not share your calculator. The use of cell phones or any other electronic devices (besides calculators) is prohibited. All such gadgets must be turned off and put away throughout the exam. Do not open the exam until told to begin. You have the one entire class period to finish the exam. Put your last name on every page of the exam and on the formula sheet. You must provide explanations and/or show work legibly to receive full credit for Sections, and V. Make sure that your answers include appropriate units and significant digits. (Note: or intermediate steps in your calculation, it s best to carry more significant digits.) undamental constants and unit prefixes are on the ormula Sheet, last page. y signing below, you indicate that you understand the instructions for this exam and agree to abide by them. You also certify that you will personally uphold the university s standards of academic honesty for this exam, and will not tolerate any violations of these standards by others. Unsigned exams will not be graded. Signature: UGACard #: Copyright c 2018 University of Georgia. Unauthorized duplication or distribution prohibited.
Section V (onus) Score /20 /80 / /10 : Multiple-Choice Questions (20 points) or each question below, choose the single best response and write the corresponding capital letter in the box provided. There is no penalty for guessing the wrong answer. 1. A wire of some length L and with a circular cross-section of diameter D, made out of a material with an electrical resistivity ρ, has a resistance of 250 kω. What will be the resistance of a wire of length 24L and diameter 2D, made from a different material, with a resistivity 3ρ? A. 1500 kω. 4500 kω C. 166.67 kω D. 300 kω. 75 kω 2. A piece of straight wire carrying a current,, is subjected to a uniform magnetic field,. Which one of the following figure panels could correctly represent the wire, its current flow direction, the -field direction and direction of the magnetic force,, exerted on the wire by the magnetic field? ig. 3.53 (A) () (C) (D) () A.. C. D.. Copyright c 2018 University of Georgia. 2
3. A molecular ion beam containing four different types of ions, called P, Q, R and S here. The beam enters a uniform magnetic field, as shown in drawing below, with 0 above the lower horizontal line, and perpendicular to, and pointing out of, the plane of the drawing. The incident straight beam is in the plane of the drawing. ig. 3.15 (out) R Q P S =0 The diameters of the semicircular ion trajectories in the -field, denoted by d P, d Q, d R and d S, respectively are observed to be in a ratio of d S : d R : d Q : d P = 4 : 3 : 2 : 1, as indicated in the drawing. Assume all four ion types carry the same absolute amount of charge per ion, q, and they all enter the -field with the same kinetic energy K. (Hint/Warning: K = 1 2 mv2. xpress v in terms of K!) What is the ratio of the ion masses, denoted by m P, m Q, m R and m S, respectively? A. m S : m R : m Q : m P = 4 : 3 : 2 : 1.. m S : m R : m Q : m P = 1 1 4 : 3 1 : 2 1 : 1. C. m S : m R : m Q : m P = 16 : 9 : 4 : 1. D. m S : m R : m Q : m P = 1 : 1 : 1 : 1. 3 2 1. m S : m R : m Q : m P = 4 : 3 : 2 : 1. Copyright c 2018 University of Georgia. 3
4. Three different circuits, Z, Y and X, are built with the same three resistors,,, and, and the same battery of battery voltage, as shown in the drawing. Compare and rank the magnitude of the voltage drops V 1 across, observed in the three different circuits. ig. 3.33 o 3 o 1 o 2 2 2 3 1 3 1 (Z) (Y) (X) A. V 1 (Y ) < V 1 (X) < V 1 (Z). V 1 (X) < V 1 (Z) < V 1 (Y ) C. V 1 (Z) < V 1 (X) < V 1 (Y ) D. V 1 (Z) < V 1 (Y ) < V 1 (X). V 1 (X) < V 1 (Y ) < V 1 (Z) Copyright c 2018 University of Georgia. 4
: Circuit Analysis (80 points) p o a 1 2 x C C y 3 R C 4 R 4 n the circuit shown below, assume that 1 = 4A 4 = 8A = 7Ω = 6Ω = 8Ω C = 80 µ. Also assume that the capacitor is fully charged, by the voltage drop across it, the left capactor plate carries a charge of Q = +640µC and there is no current ig. 3.50 flowing to or from either capacitor plate. q b (a) ind the electric potential difference, V x V y, between check points x and y. (b) ind the total current, o. [Hint: Use a loop to find 2, then a junction to find o.] (c) ind the battery voltage. [Hint: Use a junction to find 3, then a loop to find.] (d) How much heat is generated in resistor R C during 1 hour? Copyright c 2018 University of Georgia. 5
Work Space for Problem : Copyright c 2018 University of Georgia. 6
V: More Magnetic orce (10 points, onus) A piece of straight wire, 1.0m in length and carrying a current, = 4.5A, is subjected to a uniform magnetic field,. The magnetic field vector,, points into the plane of the drawing, and the current flows lies in the plane of the drawing, as shown below. The angle enclosed between current flow direction and the +x-direction is 65 o. The strength of the magnetic force,, acting on the wire is = 9.0mN. ig. 3.79 y x z (a) ind the strength of the magnetic field,. (b) ind angles, θ x, θ y and θ z, enclosed between the force vector,, and, respectively, the +x-direction, +y-direction and +z-direction. Copyright c 2018 University of Georgia. 7