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Unformatted text preview: Solutions Test 1 PHYS 1004 Summer 2010 1. The Coulomb’s force between two protons is F = 3 ∗ × 10- 8 N when the distance between them is ( in m) F c = k ( e ) 2 /r 2 so r = q ke 2 /F = 8 . 76 × 10- 11 . 2. A metallic sphere of radius 20 cm is charged to surface charge density η = 0 . 885 nC/m 2 . The electric field just outside the sphere is (in N/C) a) 10 b) 100 c) 1000 d) 10000 e) 1 E = kQ/R 2 = k 4 πR 2 σ/R 2 = 100 N/C 3. Two light plastic balls ( m=2.0 g) are hanging on two light strings (L= 20 cm). They are each charged with the same unknown charge. As a result they are separated for d = 4.0 cm. The overall charge on the system (2q) is tan( θ ) = F c / ( mg ) = d/ (2 ∗ q ( L 2 − d 2 / 4)). Solving for q gives q = 19 nC and 2 q = 38 nC so the closest answer is 53 nC . 4. A closed Gaussian surface in the shape of a cube, is placed at the origine of a coordinate system (cf. diagram). The electric field is given by E= (0, 200, 0) (inN/C). The charge inside the cube is The field is constant so q=0.The field is constant so q=0....
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This note was uploaded on 09/27/2010 for the course STAT 104157 taught by Professor Jhonbran during the Spring '09 term at California Coast University.
- Spring '09