Soln2 – Electric Fields

Soln2 – Electric Fields - 8B Worksheet...

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8B Worksheet Answers 2. Electric Fields 1. a) Red: Forces Blue/Dark Blue: Trajectories b) All three protons initially speed up. The initially stationary electron and the initially upward-moving electron also initially speed up. c) Only the initially right-ward moving electron initially slows down. The neutrons neither speed up nor slow down, but continue moving with their initial velocity (Newton’s first law!) d) The rightward moving electron initially has a speed v 0 and experiences a leftward force of constant magnitude F = qE . The acceleration, then, is a = qE/m e , which is also constant. The time it takes to stop, then, is Δ t = m e v 0 / qE . In this time, it has traveled a distance Δ x = m e v 0 2 / 2 qE . 2. a) Neither dipole (i), (ii), nor (iii) will feel a net force, and so will not translate, speed up, or slow down. The electric field at the positive end of dipole (iv) is stronger than the field at the negative end, and so dipole (iv) will accelerate to the right . Dipoles (i) and (iii), being not parallel to the electric field, will experience a net torque which will cause them to rotate . Because of their orientations, both (i) and (iii) will begin to rotate in a clockwise fashion. Neither dipoles (ii) nor (iv) experience a net torque, and thus will not rotate. However, both are in unstable configurations, and a small disturbance will cause them to rotate until the positive end is on the righthand side. b) For dipoles (i) and (iii), the maximum rotational kinetic energy occurs when the
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This note was uploaded on 10/16/2010 for the course PHYS 8B taught by Professor Catherinebordel during the Spring '10 term at University of California, Berkeley.

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Soln2 – Electric Fields - 8B Worksheet...

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