# HW2soln - Physics 21 Fall 2007 Solution to HW-2 21.2...

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Physics 21 Fall 2007 Solution to HW-2 21.2 Lightning occurs when there is a flow of electric charge (principally electrons) between the ground and a thundercloud. The maximum rate of charge flow in a lightning bolt is about 20,000 C/s; this lasts for 100 μ s or less. (A) How much charge flows between the ground and the cloud in this time? (B) How many electrons flow in this time? 21.6 Two small spheres placed 20.0 cm apart have equal charge. How many excess electrons must be present on each sphere if the magnitude of the force of repulsion between them is 4.57E-21 N? 21.23 Four identical charges Q are placed at the corners of a square of side L . Find the magnitude of the total force exerted on one charge by the other three charges. 21.86 In an inkjet printer . .. the ink drops have a radius r and travel toward the paper at a velocity v _0. The drops pass through a charging unit that gives each drop a positive charge

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HW2soln - Physics 21 Fall 2007 Solution to HW-2 21.2...

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