PracFinal-s06

# PracFinal-s06 - Physics 126: Practice Final This practice...

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1 Physics 126: Practice Final This practice final was the final exam given during Winter 2006. The median score on this exam was 13/20. This is a closed-book exam lasting 120 minutes. You may use a calculator and a 8.5 x 11 “crib sheet.” The exam contains 20 multiple-choice questions. Useful Physical Constants: Acceleration of gravity g = 9.8 m/s 2 proton charge e = 1.602 × 10 -19 C Electron mass m e = 9.1 × 10 -31 kg Proton mass m p = 1.7 × 10 -27 kg Permittivity of free space ε 0 = 8.85 × 10 -12 C 2 /(N m 2 ) Coulomb’s law constant k = 1/(4 πε 0 ) = 8.99 × 10 9 N m 2 /C 2 Permeability of free space μ 0 = 4 π × 10 -7 T m/A Speed of light in vacuum c = 3.00 × 10 8 m/s Planck’s constant h = 6.626 × 10 -34 J s Before you begin: 1. Fill in your name and section number on your Scantron sheet. Fill in your 8-digit UM ID (not your SSN) in the space indicated. 2. Fill in the version number of your exam in the area of the Scantron marked “Form.” Your exam version number is 1 . 3. Sign and date your Scantron.

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2 1. Four charges are laid out a square of edge length D = 0.2 meters as shown below. 1 2 3 4 D = 0.2 m Q = 5 ! 10 " 6 C Q = 5 ! 10 " 6 C q q Identical charges Q = +5 micro-coulombs are placed on corners #1 and #3. There is a charge q on corner #2 and an identical charge q on corner #4. The net force is zero on the charges on corners #2 and #4 . From this, find the sign and the magnitude of q. A) q = ! 2.83 " 10 ! 6 C B) q = + 2.83 ! 10 " 6 C C) q = ! 14.14 " 10 ! 6 C D) q = + 14.14 ! 10 " 6 C E) q = ! 5 " 10 ! 6 C
2. A very large surface carries a positive charge Q uniformly distributed over its 3 × 3 meter area A. Near the center of that surface there is a vertical, insulating rod that provides a guide for the vertical motion of a small bead that has a mass of m = 5 ! 10 " 3 kg and carries a positive charge q = + 5 ! 10 " 8 C . The electric field produced by charge Q is sufficient to support the bead as if it were floating on air. mass m charge q Large surface of area A that isuniformly charged Visual hint for calculation of the electric field near a large, uniformly charged sheet: ! E ! E Find the value of Q that is necessary to sustain the levitation of the bead. A)

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## This note was uploaded on 02/11/2010 for the course PHYSICS 126 taught by Professor Amidei during the Winter '08 term at University of Michigan.

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PracFinal-s06 - Physics 126: Practice Final This practice...

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