Phy102&05-s-ms1

# Phy102&05-s-ms1 - Kuwait University Physics 102 Physics...

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Kuwait University Physics Department Physics 102 First Midterm Exam (Summer Semester) July 7, 2005 Time: 10.30 to 12.15 p.m. ------------------------------------------------------------------------------------------------------------ Name…………………………………Student No.…………… Instructors: Drs. Bhatia, Farhan, Lajko, Marafi, Rakhshani, Razee, Sharma Fundamental Constants k == × 1 4 9.0 10 N m / C o 92 2 πε (Coulomb constant) ε o = 8.85 × 10 -12 C 2 / (N · m 2 ) (Permittivity of free space) e = +1.60 × 10 -19 C (Elementary unit of charge) N A = 6.022 × 10 23 (Avogadro’s number) g = 9.8 m/s 2 (Acceleration due to gravity) m e = 9.11 × 10 -31 kg (Electron mass) m p = 1.67 × 10 -27 kg (Proton mass) Prefixes of units m = 10 -3 µ = 10 -6 n = 10 -9 p = 10 -12 k = 10 3 M = 10 6 G = 10 9 T = 10 12 For use by Instructors only Prob. 1 2 3 4 5 6 7 8 9 10 Total Marks

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1. How many electrons must be removed from a conducting sphere (radius 15 cm) in order that it applies a force of 0.23 nN to a proton placed 85 cm far from its surface? a) 1.0 x10 13 b) 1.2 x10 13 c) 2.0 x10 16 d) 1.0 x10 18 e) 1.6 x10 19 2. Three point charges are held along the x-axis as shown (q = 5 nC, a = 10 cm). What is the direction (with respect to +x axis) of the net electric field at point (0, a)? a) -55 º b) +125 º c) +45 º d) +135 º e) -45 º The proton is at 0.85+0.15 m = 1 m distance from the center of the sphere. The Gauss’ law (or The Shell theorem 1) gives the electric field at this distance as a point like electric field: 2 r kQ E = The force acting between the sphere and the proton is eE qE F = = 2 10 23 . 0
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Phy102&05-s-ms1 - Kuwait University Physics 102 Physics...

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