Final Exam PHY 2140 Row Seat Date 2003 Please type your name here Please type your student number here Instructions The following procedure must be followed in order to correct any unlikely mistakes in the grading 1 Do all the questions Show your work to receive credit I must be able to understand what you have done while I am reading the exam not when you explain it to me after the exam is graded and returned 2 For each problem a write down any formula s used b justify why you used that particular formula s c copy the answer you have circled from the exam pages to the General Purpose Answer Sheet and fill in the ovals d show your work No work no point 3 The formula sheet is on the last page of the exam You may detach it from the rest of the exam I have read and understood the statement above Your signature NAME 1 Determine the point nearest the charges where the total electric field is zero Take the 6 00 C charge to be at the origin of the x axis 2 00 m a b c d e 1 80 m 1 15 m 0 41 m 0 78 m 1 15 m 15 0 C 6 00 C 2 Find the charge on the 3 F capacitor in the following circuit a b c d e 4 F 3 F 20 C 24 C 28 C 32 C not enough information 6 F 12 V 3 Two identical parallel conducting plates of area 0 25 m2 are placed with their centers 0 0030 m apart Initially the first plate has a charge of 12 x 10 9 C and the second a charge of 18 x10 9 C The plates are then connected by a conducting wire Find the potential difference between the two plates when the charges are in equilibrium Hint first find the capacitance of the two plates a b c d e 4 1 V 8 1 V 13 V 16 V not enough information 4 What is the current through the 2 00 resistor a b c d e 0 125 A 0 250 A 0 375 A 0 500 A 0 625 A 1 2 1 15 12 V 5 A cube with an edge of length l 0 04 m is placed in a uniform magnetic field throughout the region that has components Bx 0 By 4 T and Bz 3 T Find the net flux through the cube z a Zero b 0 0064 Tm2 c 0 0048 Tm2 d 0 12 Tm2 e 0 16 Tm2 x y 6 Two long straight wires 0 004 m apart carry currents of 5 0 A and 10 A as shown Find the net magnetic field midway between the wires Take B as positive if it is going into the page a b c d e 5 0 x 10 4 T 5 0 x 10 4 T 1 0 x 10 3 T 1 0 x 10 3 T Zero 5 0 A 10 A 0 0040 m 7 As part of his stage show Ozzie Osbourne constructs a guillotine consisting of a metal blade of length 1 50 m and mass 0 50 kg that can slide without friction along rails To slow down the metal blade the rails are placed in a 2 00 T magnetic field and can carry current Find the velocity of the blade assuming that there is no net force on the bar and that the resistance R 1 00 Hint the current through the resistor depends on the velocity of the blade R a 0 54 m s B b 0 76 m s I c 1 25 m s d 4 79 m s e At long last the Prince of Darkness meets the Prince of Darkness v 1 50 m 8 After the concert Kid Rock presents a golden neck brace to his hero Ozzie Osbourne To impress him he spins the brace about a vertical axis at a frequency of 60 Hz in a magnetic field of B 0 5 T as shown If the area of the brace is 5 0 x 10 3 m2 calculate the maximum emf induced in the brace a b c d e 0 76 V 0 94 V 1 18 V 1 27 V none of the above 9 If the kinetic energy of a rocket ship is three times its rest energy what is its speed a b c d e 0 72c 0 87c 0 94c 0 97c none of the above 10 When light of wavelength 350 nm falls on a potassium surface electrons are emitted that have a maximum kinetic energy of 1 31 eV Find the work function of potassium a b c d e 2 24 eV 4 42 eV 6 24 eV 8 84 eV none of the above 11 A hydrogen atom is in the first excited state n 2 Using the Bohr theory of the atom find the kinetic energy of the electron a b c d e 1 2 eV 3 4 eV 5 4 eV 6 8 eV 13 6 eV B 12 What is the energy of the photon that when absorbed by a singly ionized transition from n 1 to n 4 a b c d e 4 2 He atom can cause a 4 6 eV 14 2 eV 51 0 eV 108 eV none of the above 13 A long straight wire carries a steady current I A rectangular conducting loop lies in the same plane as the wire with two sides parallel to the wire and two sides perpendicular Suppose the loop is pushed toward the wire as shown Given the direction of I the induced current in the loop is a clockwise b counterclockwise c need more information 14 A cylindrical piece of insulating material is placed in an external electric field as shown The net electric flux passing through the surface of the cylinder is a negative b positive c zero 238 15 Find the mass density of nucleons in a 92 U nucleus The volume of a sphere is 4 r3 3 Assume that the proton and the neutron have the same mass m 1 67 x 10 27 kg a b c d e 2 3 x104 kg m3 2 3 x109 kg m3 2 3 x1012 kg m3 2 3 x1015 kg m3 2 3 x1017 kg m3 16 A metal wire has a resistance of 10 00 at a temperature of 20 C If the same wire has a resistance of 10 55 at 90 C what is the resistance when its temperature is 20 C Hint first find the temperature coefficient of resistivity a 0 70 b 9 69 c 10 31 d 13 8 17 A physics professor can teach as long as 60 of his brain cells are alive and functioning The stress of teaching causes brain cells to die with an average half life of 30 years Assume that brain cells don t reproduce or repair themselves and that there is …
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