PY 208 Practice Test 2 Spring 2009 Note: THIS TEST IS LONGER THAN THE ACTUAL TEST. It is a sample and does not include questions on every topic covered since the start of the semester. Also be sure to reviewhomework assignments on Webassign White board problems worked in the lab Exercises, Examples, and Review Questions (at the end of each chapter)in your textbook Name (print) __________________________________ When you turn in the test, including the formula page, you must show an NCSU photo ID to identify yourself. Do not use other paper. If you need more space, write on the blank page included at the end of the test, and indicate that you did this. • Read all problems carefully before attempting to solve them. • Your work must be legible, and the organization must be clear. • You must show all your work, including correct vector notation. • Correct answers without adequate explanation will be counted wrong. • Incorrect work or explanations mixed in with correct work will be counted wrong. Cross out anything you don’t want us to read! • Make explanations complete but brief. Do not write a lot of prose. • Include diagrams! • Show what goes into a calculation, not just the final number: ( )( )()()44563105104102105108xxxxxdcba==⋅⋅−− • Give standard SI units with your results Unless specifically asked to derive a result, you may start from the formulas given on the formula sheet, including equations corresponding to the fundamental concepts. If a formula you need is not given, you must derive it. If you cannot do some portion of a problem, invent a symbol for the quantity you can’t calculate (explain that you are doing this), and use it to do the rest of the problem. Problem 1 Problem 2 Problem 3 Problem 4 Problem 5 Total SIGN THE HONOR PLEDGE: I have neither given nor received unauthorized aid on this test. ----------------------------------------------------------------------------------------------- Sign your name on the line above.1. Two thin glass rods, each 3 meters long, are rubbed all over with silk. Each rod acquires a charge of +3x10-7 C. The rods are arranged at right angles to each other, as shown in the diagram, The rods lie in the xy plane; the origin is at the base of the vertical rod, as shown. (a) What is the net electric field at location C, at <1.5, 1.5, 0> m, marked by the “x”? Express your answer as a vector. Clearly show all steps in your work. A In the following questions, if a quantity is zero, state this explicitly. (b) A neutral copper block is now placed so location C is inside the block. Draw the approximate distribution of charge in and/or on the copper block, following the conventions for diagrams used in the textbook and in class. (c ) Draw an arrow representing the electric field at location C, inside the copper block, due only to the two charged rods. Label this arrowrodsEr. (d) Draw an arrow representing the electric field at location C, due only to the charges in and/or on the copper block. Label this arrow . copperEr (e) Draw an arrow representing the net electric field at location C.2. A capacitor consists of plates 3 m in radius, separated by a distance of 6 mm. The left plate of the capacitor has a charge of -7x10-7 C. (a) What is the potential difference VC – VB? Show all steps in your work. (b) What is the potential difference VB – VA? Show all steps in your work. (c) What is the potential difference VC – VA? Show all steps in your work. (d) A moving electron enters the capacitor through a tiny hole in the right plate. Its initial velocity is such that it passes through location A, and a short time later it reaches location C. What is the change in kinetic energy of the electron between location A and location C? (Remember that the gravitational force on the electron is negligible compared to electric forces.) Show all steps in your work.3. The arrangement of charged particles shown in the diagram is called an electric quadrupole. At locations on the x-axis far from the quadrupole, the electric field due to the quadrupole has the form: 0,0,414xhEoπε=r (h is a constant with units C·m2, combining the magnitude of the charges and their separations). The diagram below is not drawn to scale; both locations A and B are far from the quadrupole. The origin is at the center of the quadrupole. (a) At two locations A and B, draw arrows showing the electric field at that location. The relative magnitudes of the arrows should be correct (longer arrows means larger magnitude). (b) Is VB – VA positive, negative, or zero? Briefly but clearly explain your reasoning: c) What is VB – VA ? Your answer should be a symbolic (algebraic) expression, which may include the constants h, a, b, and 1/(4πєo). Show all steps in your work.4.In a circuit in the steady state, 3.5x1017 electrons enter a particular wire each second, flowing in the –x direction. What is the magnitude and direction of the conventional current in this wire? Show your work. 5. An electron moves in the +y direction with a speed of 3x106 m/s, as shown in the diagram. At a particular instant the electron is at <2x10-8, 1.5x10-8, 0> m. The location D is at <−1.0x10-8, -1.5x10-8, 0> m. (a) Find the direction and magnitude of the electric field at location D, due to the electron. Your answer should be expressed as a vector. Show all your work. b) Find the direction and magnitude of the magnetic field at location D, due to the electron. Your answer should be expressed as a vector. Show all your work.6. Four voltmeters are connected to a circuit as shown. As on the voltmeter you used in lab, if the negative lead (black, COM) is attached to a location at lower potential than the positive (red) lead, the voltmeter reading is positive. The circuit contains two devices whose identity is unknown, and a capacitor. The separation between the plates of the capacitor is 3 mm. At a particular moment, the readings observed on the voltmeters are: Voltmeter A: −2.5 V Voltmeter B: +9 V Voltmeter C: −3.0 V (a) At this moment, what is the reading on voltmeter D, both magnitude and sign? Briefly explain your reasoning. (b) On the diagram draw an arrow indicating the direction of the electric field at a location inside the capacitor. Label the arrow Er. (c) What is the magnitude of the electric field inside the capacitor?