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PY208 Matter & Interactions Final Exam S2005 Name (print)_________________________________________Please circle your lecture section below: 003 (Ramakrishnan 11:20 AM) 004 (Clarke 1:30 PM) 005 (Chabay 2:35 PM) 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 the 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’re doing this), and use it to do the rest of the problem. Problem 1 (15 pts) Problem 2 (20 pts) Problem 3 (25 pts) Problem 4 (10 pts) Problem 5 (15 pts) Problem 6 (30 pts) Problem 7 (20 pts) Problem 8 (30 pts) Total (165 pts) Make sure that no pages are missing from your test, and each problem listed above appears on your test. SIGN THE HONOR PLEDGE: I have neither given nor received unauthorized aid on this test. ___________________________________________________________________ Sign your name on the line above208 Problem 1 (15pts) Two dipoles are oriented as shown in the diagram. Each dipole consists of two charges+6 nC and −6 nC, held apart by a rod of length 1.5 mm (nC = nanocoulomb = 1e-9 coulomb). The location marked x is 8 cm from the center of each dipole. 8 cmdipole 2dipole 1 The relative lengths of your arrows for parts a, b, and c below must be correct. If any of the quantities asked for is zero you must state this explicitly. (a: 2pts) On the diagram draw an arrow representing the electric field vector at the location marked x due to dipole1 and label it 1Er. (b: 2pts) On the diagram draw an arrow representing the electric field vector at the location marked x due to dipole 2 and label it 2Er. (c 2pts): On the diagram draw an arrow representing the net electric field vector at the location marked x and label it netEr. (d: 2pts) A small ball carrying a charge of +7 nC uniformly distributed over its surface is placed at the location marked “x”. Draw an arrow representing the net electric force on the ball and label it Fr. (e: 7pts) What is the magnitude of the net electric force on the ball? Show your work.208 Problem 2 (20 pts) A solid metal ball of radius 1.2 cm with a charge of -15 nC is located near a hollow plastic ball of radius 2.3 cm that has a uniformly distributed charge of −6 nC on its outer surface. The distance between the centers of the balls is 9 cm. The relative lengths of your arrows must be correct. If any quantity is zero you must state this explicitly. (a: 9 pts) Sketch the approximate charge distributions on and/or in the plastic ball and the metal ball. (b: 2pts) Draw an arrow representing the electric field vector at the center of the metal ball due to the plastic ball alone. Label it plEr. (c: 2pts) Draw an arrow representing the electric field vector at the center of the metal ball just due to the charges on the metal ball. Label itmEr. (d: 2pts) Draw an arrow representing the net electric field vector at the center of the metal ball. Label it netEr. (e: 5pts) Calculate the electric field at the center of the metal ball due only to the charges in and/or on the metal ball. Show your work. metal plastic208 Problem 3 (25 pts) Two nichrome wires of different thickness are part of a larger steady state circuit that is not shown on the diagram. A conventional current of 6 amperes flows to the right through the thicker wire. The thicker wire has a diameter of 0.34 mm and a length of 20 cm. The thinner wire has a diameter of 0.13 mm and a length of 30 cm (the diagram is not drawn to scale). Nichrome has 9e28 electrons/m3 and the electron mobility is 7e-5 (m/s)/(N/C). Calculate the potential difference VA – VB, both magnitude and sign. Show your work. AB20 cm30 cmconnecting wiresnot shownconnecting wiresnot shown(Diagram is not to scale: diameter of wires is greatly exaggerated.)208 Problem 4 (10 pts). You measure the potential differences between some of the locations shown at the right, and find that VA – VB = –11 volts VB – VC = +7 volts VC – VD = +5 volts (a: 5pts) What is VD – VA? Show your work. (b: 5pts) What is VB – VD? Show your work. ABCD208 Problem 5 (20 pts) A coil of wire of radius 3 cm, with 17 turns of wire, is located on the –x axis, a distance of 15 cm from the origin. A current of 2.5 amperes runs through the coil in the direction shown on the diagram. A compass is located at the origin. Magnetic North is in the –z direction, as shown on the diagram. Calculate the compass deflection, both magnitude and direction. Show your work. coilcompassto batteriesNorthxyzI208 Problem 6 (30 pts) A large circular metal disk of radius 1.7 m has a charge of 3µC (µC = 1e-6 C). A long straight wire connected to a power supply is located near the charged disk. The disk and the wire are placed near a source which produces a beam of electrons with a speed of 5e5 m/s in the +x direction. Note that only the wire, the disk and a single electron (for simplicity) are shown in the diagram. The wire is much longer and the disk much larger than are shown in the diargram. disk +3µCwire When the power supply is not turned on, so there is no current running through the long wire, the electrons follow a curved path (dotted lines in the diagram) and


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SEWANEE PHYS 104 - Matter and Interactions

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