Sp04-MT2-Smoot-Exam+Soln - Department of Physics,...

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Unformatted text preview: Department of Physics, University of California, Berkeley Mid-term Examination 2 Physics 7B, Section 2, Prof. Smoot 6:00 pm - 8:00 pm, 6 April 2004 Name: SID No: Discussion Section: Name of TA: Problem 1 Problem 2 Problem 3 Problem 4 Problem 5 Problem 6 Problem 7 Problem 8 Score: 1 Answer all problems. Write clearly and explain your work. Partial credit will be given for incomplete solutions provided your logic is reasonable and clear. Cross out any parts that you dont want to be graded. Enclose your answers with boxes. Express all numerical answers in SI units . Answers with no explanation or disconnected comments will not be credited. If you obtain an answer that is questionable, explain why you think it is wrong. Constants and Conversion factors Charge of electron e 1 . 6 10- 19 C Avogadro number, N A 6 . 022 10 23 Permittivity of vacuum, 8 . 85 10- 12 F m- 1 Universal gas constant, R 8.315 J mol- 1 K- 1 = 1.99 cal mol- 1 K- 1 Boltzmann constant, k 1 . 381 10- 23 J K- 1 Stefan-Boltzmann constant, 5 . 67 10- 8 W m- 2 K- 4 Acceleration due to gravity, g 9.8 m s- 2 Specific heat of water 1 kcal kg- 1 C- 1 Heat of fusion of water 80 kcal kg- 1 1 atm 1 . 013 10 5 N m- 2 1 kcal 4 . 18 10 3 J 1 hp 746 W 1 liter 10 3 cm 3 Some useful equations Coulomb s law : F = 1 4 q 1 q 2 r 2 r Electric field : d E = 1 4 dq r 2 r Electric dipole : p = q d T orque on a dipole : ~ = p E P otential energy of a dipole : U =- p E Gauss s law : I E d A = q encl P otential difference : V ab =- Z b a E d l P otential : dV = 1 4 dq r P otential energy : U ab = qV ab Electric field and potential : E =- V Capacitance : C = q V ab 2 Capacitors in series : 1 C eq = X 1 C i Capacitors in parallel ; C eq = X C i Energy stored in a capacitor : U = 1 2 CV 2 Energy density : u = 1 2 E 2 Current : I = dq dt Current and current density : dI = j d A Ohm s law : V = IR Ohm s law : j = E Resistivity and resistance : R = l A Electric power ( DC ) : P = V I Average electric power ( AC ) : P = 1 2 I 2 R rms current : I rms = 1 2 I Resistors in series : R eq = X R i Resistors in parallel : 1 R eq = X 1 R i Kirchhoff current rule : X I = at a node Kirchhoff potential rule : X = X IR around a loop V = V x x + V y y + V z z V = V r r + 1 r V + V z z V = V r r + 1 r V + 1 rsin V Some useful Integrals: Z dx x 2 + a 2 = log x + x 2 + a 2 or sinh- 1 x a Z dx x 2 + a 2 = 1 a arctan ( x a ) Z dx ( x 2 + a 2 ) 3 / 2 = x a 2 x 2 + a 2 3 1. [25 points] Short Questions (a) [5 points] Circle (black in) T or F for True or False T F (i) Unlike electric charges attract and like charges repel....
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This note was uploaded on 02/04/2010 for the course PHYSICS 7B taught by Professor Packard during the Spring '08 term at University of California, Berkeley.

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Sp04-MT2-Smoot-Exam+Soln - Department of Physics,...

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