X2.4a 115PHYS-115(4) (Kaldon-26364) Name __________S O L U T I O N_________WMU - Spring 2005Exam 2A - 100,000 points Book Title ________________________________________________Rev. 02/23/05 We.A4State Any Assumptions You Need To Make – Show All Work – Circle Any Final AnswersUse Your Time Wisely – Work on What You Can – Be Sure to Write Down EquationsShort Answers Should Be Short! – Feel Free to Ask Any QuestionsEXAM 2 [FORM - A]PHYS-115 (KALDON-4)SPRING 2005WMUOersted, Hans Christian (ör´stĭð), 1777–1851, Danish physicist and chemist.His discovery that a magnetic needle is deflected by a conductor carrying an electriccurrent showed a relation between ELECTRICITY and MAGNETISM and initiated thestudy of electromagnetism. (One of the) unit(s) of magnetic field strength, the oersted,is named for him. Oersted was the first to isolate ALUMINUM.Energy, 1819Danish physicist Hans Christian Oersted, 42, advances knowledge of electromagneticenergy. He notices that a compass needle located close to a wire carrying an electriccurrent will swing wildly but will finally settle at right angles to the wire. He suspectsthat the current in the wire must set up a magnetic field around it, and his observationwill be the starting point for others (see ROMAGNOSI, 1802; AMPÈRE, 1820;FARADAY, 1821; ELECTROMAGNET, 1823).Microsoft Bookshelf '95mp07410=´ ×-Tm A/Physics 115 / Exam 2 Spring 2004 Page 2This is the Story of Four Resistors Living in the Big City… Circuit City… (50,000 points)1.) Consider four identical 625 W resistors and a 16.55 volt battery. Find (a) the maximum and (b) theminimum equivalent resistance you can make with these resistors. Be sure to draw the circuit diagrams for fullcredit.(a) Maximum = Series (b) Minimum = ParallelRRRRRReq=+++== =123444625 2500WWbg.1 1111446254156 31234RRRRRRRReqeq=+++ === =WW.(c) Our four identical 625 W resistors and our 16.55 volt battery are hooked up in the circuit as shown. Find theequivalent resistance of the circuit, R1234 , by reducing the resistor network.Series Parallel Series Done!RRRRRRRRRR23 2 3234 23 42341234 1 2342 625 1250111 112501625416 7625 416 7 1042=+= ==+= +==+ = + =WWWWWWWWbg....(d) Find the current, Itotal , and the power dissipated, Ptotal , of the equivalent circuit. If you did not get ananswer to (c), use Req = 1625 W.VIRIVRvoltsA=== =16 5510420 01588..WP IV A volts W== =0 01588 16 55 0 2628...bgbgPhysics 115 / Exam 2 Spring 2004 Page 3(e) An RC circuit consists of a 625 W resistor and a 625 mF capacitor. Find the time t in seconds it takes for thefully charged capacitor to discharge to half its initial value, i.e. q = 0.500 Qmax .t == ´ ======-=-===-----RC FqQe q QQQeeetRCtRCtRCtRCtRCtRC625 625 10 0 39060500050005000500069310 6931 0 6931 0 3906027076Wbgchdibgbgbgbg.sec;...ln ln .....sec.secWait A Second! How’d Oersted Do It? SEE COVER SHEET (50,000 points)2.) Yesterday afternoon, after PHYS-115 class, after my 4pm appointment, after the rest of the Physics Dept.meeting, one of my colleagues came in and showed me a problem in a Physics Education book and he didn’tunderstand how they could get the answer they did. I looked at it, at first agreed with him, and then realizedthat Real Life isn’t as simple as we make it in class sometimes. Consider: Oersted runs a current through awire and a compass needle changes its direction. The North end of a compass needle points in the samedirection as a magnetic field points (N points towards S). (a) A current carrying wire is shown below, in twoviews. Show by R.H.R. which way the magnetic field from the wire points at the P in both views.View From Above View Looking From Right SidePhysics 115 / Exam 2 Spring 2004 Page 4(b) A compass needle points to the LEFT while you are sitting in 1104 Rood Hall. Butfrom part (a), there’s no way that the B-field from the wire could deflect the needle atpoint P. But… a real compass is thick. The needle would sit ABOVE the wire – andthere WOULD be a magnetic field. Okay, okay. Enough of Dr. Phil marveling at thewonder of Physics… Suppose the compass sits directly ON TOP of the wire. For a wirecarrying a current of 1.00 A, find the distance d where the magnetic field measures B =0.000100 T. (This is 1/10,000th of a Tesla or 1.00 Gauss, the same strength as theEarth’s magnetic field here on the surface.) BIrIddIBTm A ATmmm====´×==-mpmpmppp0007222410 1002 0 0001000 002000 2 000/....chbgbgbg(c) A coil consists of 10,500 turns of wire in a length of 15.0 cm and a diameter of 8.00 cm. The B-field in thesolenoid measures B = 0.00135 T, as shown. Find the magnitude of the current I in the coil and indicatewhether the current comes out the LEFT or the RIGHT of the coil.BNIIBNTmTm AA===´×=-mmp0070 00135 0150410 105000 01535ll../,.bgbgchbg(d) For the same solenoid coil as in (c), with B = 0.00135 T, a second wire is inserted down the center of thecoil. If the current in this second wire is i = 0.500 A as shown, find the magnitude and direction of the magneticforce, FB , on this second wire. Use the length of the coil as the length of the second wire.(Alternately, the second current, i2 , is everywhere in the coilperpendicular to the first current, i1 , and therefore there isno magnetic force between perpendicular wires.)(e) The E-field part of a velocity selectorconsists of two parallel plates, separated bya gap d = 0.100 m and with a potentialdifference DV = 1500. volts. If the B-fieldpart uses the same solenoid coil with B =0.00135 T as above, find the “designspeed” v for this velocity selector, usingany charged particle.rrBi and are anti - parallelFB\=0DDVEdEVdvoltsmVmvEBVmTms ms=== === = ´ =1500010015 00015 0000 001351111 10 11110