PHYS 101 Study Guide - Midterm Guide: Relative Permittivity, Kinetic Energy, Net Force
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Phy2049 exam #1 solutions fall 2012: two identical conducting spheres a and b carry equal charge q. They are separated by a distance much larger than their diameters. A third identical conducting sphere c carries charge. Sphere c is first touched to a, then to b, and finally removed. As a result, the electrostatic force between a and b, which was originally f, becomes: After c touches a, (cid:1)(cid:2) = (cid:1)(cid:4); (cid:1)(cid:2) + (cid:1)(cid:4) = 3(cid:1) (cid:1)(cid:2) = (cid:1)(cid:4) = (cid:9)(cid:10) (cid:11) . (cid:11) (cid:1)(cid:13) = (cid:1) (cid:4) = (cid:15)(cid:10) Then c touches b, (cid:1)(cid:13) = (cid:1) (cid:4); (cid:1)(cid:13) + (cid:1) (cid:4) = (cid:15)(cid:10) (cid:16) . The x and y components of coulomb force on q2 are (cid:17)(cid:27) = 24(cid:30)(cid:31)(cid:11) (cid:11)(cid:11) = 1. 54 10%(cid:24)&"; (cid:17)( = 2(cid:30)(cid:31)(cid:11) (cid:24)(cid:11) = 0. 51 10%(cid:24)&". The net force is (cid:17) = )(cid:17)(cid:27)(cid:11) + (cid:17)((cid:11) = 1. 6 10%(cid:24)&": four charges are at the corners of a square, with b and c on opposite corners.
