MasteringPhysics: Assignment Print View file:///c:/Documents%20and%20Settings/lbr/Desktop/HW3_files/ass. .. 1 of 18 9/21/2006 9:58 AM Physics 220 Assignment 3 Assignment is due at 11:59pm on Tuesday, September 26, 2006 Credit for problems submitted late will decrease to 0% over the course of 240 hour(s) after the deadline has passed. The wrong answer penalty is 1% per part. Multiple choice questions are penalized as described in the online help. There is no opened hint penalty or unopened hint bonus. You are allowed unlimited attempts per answer. This assignment is now complete. Section 3.1. Visualizing Electric Fields Description: Select the correct drawing of electric field lines for several situations and answer questions about why other choices are incorrect. Then, these ideas are demonstrated with an applet. Learning Goal: To understand the nature of electric fields and how to draw field lines. Electric field lines are a tool used to visualize electric fields. A field line is drawn beginning at a positive charge and ending at a negative charge. Field lines may also appear from the edge of a picture or disappear at the edge of the picture. Such lines are said to begin or end at infinity . The field lines are directed so that the electric field at any point is tangent to the field line at that point. The figure shows two different ways to visualize an electric field. On the left, vectors are drawn at various points to show the direction and magnitude of the electric field. On the right, electric field lines depict the same situation. Notice that, as stated above, the electric field lines are drawn such that their tangents point in the same direction as the electric field vectors on the left. Because of the nature of electric fields, field lines never cross. Also, the vectors shrink as you move away from the charge, and the electric field lines spread out as you move away from the charge. The spacing between electric field lines indicates the strength of the electric field, just as the length of vectors indicates the strength of the electric field. The greater the spacing between field lines, the weaker the electric field. Although the advantage of field lines over field vectors may not be apparent in the case of a single charge, electric field lines present a much less cluttered and more intuitive picture of more complicated charge arrangements. Part A
MasteringPhysics: Assignment Print View file:///c:/Documents%20and%20Settings/lbr/Desktop/HW3_files/ass. .. 2 of 18 9/21/2006 9:58 AM Which of the following figures correctly depicts the field lines from an infinite uniformly negatively charged sheet? Note that the sheet is being viewed edge-on in all pictures. Hint A.1
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