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Unformatted text preview: September 19, 2008 PHY2054 Discussion-Fall 08 Quiz 3 (Chapter 16.4-16.8) Name: UFID: *1. (5pts) In Rutherfords experiment, alpha particles (having charges of +2 e and masses of 6.64 10- 27 kg) were fired toward a gold nucleus with charge +79 e . An alpha particle, initially very far from the gold nucleus, is fired at 1.50 10 7 m/s directly toward the nucleus. How close does the alpha particle get to the gold nucleus before turning around? Assume the gold nucleus remains stationary. Only the electric force is exerted on the electron, thus the mechanical energy of the electron is conserved. The initial potential energy is taken to be zero due to the large distance between the two particles. The final kinetic energy is also zero because the -particle momentarily stops when it turns around. Thus we have E i = E f (1/2)mv 2 = kq 1 q 2 /r r = 2kq 1 q 2 /mv 2 = 28.9910 9 279(1.610-19 )/[6.6410-27 (1.510 7 )] = 4.8710-14 m **2. (5pts) An electron is fired into the region between two parallel conducting plates that are 2.00 **2....
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